Paper on Characterization of Pressure Composite Tubes

MECHANICAL CHARACTERIZATION OF FILAMENT WOUND COMPOSITE TUBES

BY INTERNAL PRESSURE TESTING

A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES

OF MIDDLE EAST TECHNICAL UNIVERSITY

BY

PINAR KARPUZ

IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR

THE DEGREE OF MASTER OF SCIENCE IN

METALLURGICAL AND MATERIALS ENGINNERING

MAY 2005

Approval of the Graduate School of Natural and Applied Sciences

Prof. Dr. Canan ÖZGEN Director

I certify that this thesis satisfies all the requirements as a thesis for the degree of Master of Science.

Prof. Dr. Tayfur ÖZTÜRK

Head of Department This is to certify that I have read this thesis and that in my opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Science.

Prof. Dr. Alpay ANKARA Supervisor Examining Committee Members Prof. Dr. Filiz SARIOĞLU (METU, METE)

Prof. Dr. Alpay ANKARA (METU, METE)

Assoc. Prof. Dr. C. Hakan GÜR (METU, METE)

Assoc. Prof. Dr. Cevdet KAYNAK (METU, METE)

Fikret ŞENEL, (M.S. in ME) (BARIŞ IND.)

I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last name : Pınar KARPUZ

Signature :

iii

ABSTRACT

MECHANICAL CHARACTERIZATION OF FILAMENT WOUND COMPOSITE TUBES BY INTERNAL PRESSURE TESTING

Karpuz, Pınar

M.S., Department of Metallurgical and Materials Engineering

Supervisor : Prof. Dr. Alpay ANKARA

May 2005, 104 pages The aim of this study is to determine the mechanical characteristics of the filament

wound composite tubes working under internal pressure loads, generating data for

further investigation with a view of estimating the remaining life cycle of the tubes

during service. Data is generated experimentally by measuring the mechanical

behavior like strains in hoop direction, maximum hoop stresses that are formed

during internal pressure loading. Results have been used to identify and generate the

necessary data to be adopted in the design applications. In order to determine these

parameters, internal pressure tests are done on the filament wound composite tube

specimens according to ASTM D 1599-99 standard. The test tubes are manufactured

by wet filament winding method, employing two different fiber types, two different

fiber tension settings and five different winding angle configurations.

iv

The internal pressure test results of these specimens are studied in order to determine

the mechanical characteristics, and the effects of the production variables on the

behavior of the tubes. Pressure tests revealed that the carbon fiber reinforced

composite tubes exhibited a better burst performance compared to the glass fiber

reinforced tubes, and the maximum burst performance is achieved at a winding angle

configuration of [±54°]3[90°]1. In addition, the tension setting is found not to have a

significant effect on the burst performance. The burst pressure data and the final

failure modes are compared with the results of the ASME Boiler and Pressure Vessel

Code laminate analysis, and it was observed that there is a good agreement between

the laminate analysis results and the experimental data. The stress – strain behavior

in hoop direction are also studied and hoop elastic constants are determined for the

tubes.

Keywords: composite, filament winding, internal pressure testing, burst pressure,

hoop elastic constant.

v

ÖZ

FİLAMAN SARGI TEKNİĞİ İLE ÜRETİLMİŞ KOMPOZİT TÜPLERİN İÇ BASINÇ TEST YÖNTEMİYLE MEKANİK KARAKTERİZASYONU

Karpuz, Pınar

Yüksek Lisans, Metalurji ve Malzeme Mühendisliği Bölümü

Tez Yöneticisi : Prof. Dr. Alpay ANKARA

Mayıs 2005, 104 sayfa

Bu çalışmada iç basınç yükleri altında çalışan filaman sargı tekniğiyle üretilmiş

kompozit tüplerin mekanik özelliklerinin belirlenmesi ve tasarım uygulamalarında ve

ömür çalışmalarında kullanılmak üzere gerekli verilerin elde edilmesi amaçlanmıştır.

Bu amaçla iç basınç yükleri altında malzeme içinde çevresel yönde oluşan gerinim

ve gerilimler deneysel yöntemlerle ölçülmüş ve yine deneysel maksimum patlama

basıncı verileriyle birlikte tasarım uygulamalarında kullanılabilecek şekilde

değerlendirilmiştir. Bu özelliklerin belirlenmesi için iki farklı elyaf malzemesi, iki

farklı elyaf gerilginlik değeri ve beş farklı sarım açısı konfigürasyonundan ıslak

filaman sargı yöntemiyle üretilmiş kompozit tüplere ASTM D1599-99 standardının

gereğince iç basınç deneyleri uygulanmıştır.

vi

İç basınç deney sonuçları mekanik özellikleri ve üretim parametrelerinin bu

özelliklere etkisini belirlemek amacıyla incelenmiştir. Bu deneyler sonucunda karbon

elyafla takviye edilmiş tüplerin patlama performanslarının cam elyafla takviye

edilmiş tüplere nazaran daha iyi olduğu ve maksimum patlama dayancının

[±54°]3[90°]1 sarım açısı konfigürasyonunda elde edildiği görülmüştür. Ekstra elyaf

gerginliğinin patlama performansına önemli bir etkisi tesbit edilmemiştir. Elde edilen

iç basınç patlama sonuçları “ASME Boiler and Pressure Vessel Code” lamina analiz

sonuçlarıyla karşılaştırılmış ve sonuçların uyum içersinde olduğu gözlenmiştir.

Çalışmada ayrıca tüplerin gerilim – gerinim davranışları incelenmiş ve çevresel

yöndeki elastik sabitleri de hesaplanmıştır.

Anahtar Kelimeler: kompozit, filaman sargı, iç basınç deneyi, patlama basıncı,

çevresel elastik sabit.

vii

To My Family

viii

ACKNOWLEDGMENTS I would like to thank Prof. Dr. Alpay ANKARA for his guidance, encouragement,

insight, advice and criticism throughout the research.

I also want to express my thanks to the examining committee members for their

invaluable contributions to this thesis.

I am deeply thankful to mom and dad, whose emotional strength, free-flowing love

and caring concern have helped shape my maturation. Without their patience and

support, the research period would have been a complete disaster.

I want to thank all the BARIŞ Elektrik Endüstrisi A.Ş. staff for their support. But I

want to express my special thanks to Aybars GEDİZ, Fikret ŞENEL and Gökhan

GÜVEN for their continuous concern, help and support; and their friendly and

humorous, but very kind attitude towards me all throughout this work. In addition,

the technical assistance and efforts of Hasan DEVREZ are greatly acknowledged.

Finally, I want to thank all my friends, especially to Ahmet Semih SUNKAR, for

their moral support in every occasion, thus making this study easier and more

bearable for me.

This study was supported by METU Scientific Research Project Funds; Grant No:

BAP-2004-03-08-05.

ix

TABLE OF CONTENTS

PLAGIARISM ....................................................................................................iii ABSTRACT .........................................................................................................iv ÖZ .........................................................................................................................vi DEDICATION ...................................................................................................viii ACKNOWLEDGEMENTS ................................................................................ix TABLE OF CONTENTS .....................................................................................x LIST OF TABLES ..............................................................................................xiii LIST OF FIGURES ............................................................................................xiv CHAPTER

1. INTRODUCTION .....................................................................................1 1.1 Objective Of The Study .......................................................................2

2. THEORY AND LITERATURE REVIEW .............................................4

2.1 Composites.............................................................................................4 2.1.1 Classification Of Composites .....................................................5

2.1.1.1 Metal Matrix Composites .....................................................5 2.1.1.2 Ceramic Matrix Composites .................................................6 2.1.1.3 Polymer Matrix Composites (PMC’s) ..................................6

2.1.1.3.1 Matrix Materials ........................................................7 2.1.1.3.2 Reinforcement Materials ...........................................9 2.1.1.3.3 Manufacturing Methods ..........................................12

2.2 Mechanical Characterization of Filament Wound Tubes ...............17

2.2.1 Test Methods and Their Standards ............................................17 2.2.2 Literature Survey on Mechanical Characterization of Filament

Wound Tubes ............................................................................19

x

3. EXPERIMENTAL WORK .....................................................................28

3.1 Test Tube (Specimen) Design.............................................................28 3.2 Test Setup ............................................................................................30

3.2.1 Pressure Test Setup ...................................................................30 3.2.2 Test Fixtures ..............................................................................32 3.2.3 Strain Gauge Data Acqusition System ......................................33

3.3 Specimen Manufacturing ...................................................................34 3.3.1 Filament Winding Machine .......................................................34 3.3.2 Tooling.......................................................................................35 3.3.3 Filament Winding ......................................................................36 3.3.4 Cutting the Tubes and Grinding of End Reinforcements...........39

3.4 Tube Nomenclature .............................................................................40 3.5 Strain Measurements ..........................................................................41

3.6 Testing Procedure ...............................................................................41

3.7 Testing Reporting ................................................................................42

3.7.1 Record of the Data .....................................................................43 3.7.2 Calculations ...............................................................................44

4. EXPERIMENTAL RESULTS .................................................................46

4.1 Internal Pressure Test Results ............................................................46 4.1.1 Carbon Fiber Reinforced Tubes .................................................46 4.1.2 Glass Fiber Reinforced Tubes ....................................................54

4.2 Performance Factors ...........................................................................61 4.3 Hoop Elastic Constants........................................................................64

5. DISCUSSIONS ..........................................................................................68

5.1 Burst Pressure Studies ........................................................................68 5.1.1 Effect of Winding Angle Configuration ....................................68 5.1.2 Effect of Extra Fiber Tensioning ...............................................71 5.1.3 Effect of the Type of the Reinforcement Material ....................73

5.2 Hoop Elastic Constant Studies ............................................................76 5.2.1 Effect of Winding Angle Configuration .....................................76 5.2.2 Effect of Extra Fiber Tensioning ................................................79 5.2.3 Effect of the Type of Reinforcement Material............................81

xi

5.3 Failure Modes .......................................................................................83 5.4 Comparison of the Burst Pressure Data with Laminate Analysis ..90

6. CONCLUSION AND RECOMMENDATIONS ....................................95 REFERENCES......................................................................................................100

xii

LIST OF TABLES

TABLES Table 2.1 Mechanical properties of resins …………………………………..…9

Table 2.2 Mechanical properties of commercial fibers ……………………….11

Table 3.1 Mechanical properties of the resin system employed …………...…36

Table 3.2 Mechanical properties of the reinforcements employed …………...37

Table 3.3 Measured tension values for the fibers…………..............................38

Table 4.1 The test results for carbon fiber reinforced tubes …..…...…………48

Table 4.2 The test results for glass fiber reinforced tubes…………………….55

Table 4.3 Burst performance factors for the test tubes......................................62

Table 4.4 Hoop elastic constants for the tubes..................................................65

Table 5.1 Internal pressure test and ASME Boiler and Pressure Vessel Code,

Section X analysis results .…………………. ……….……….....…91

Table 6.1 Mechanical properties of carbon fiber reinforced tubes …………...96

Table 6.2 Mechanical properties of glass fiber reinforced tubes …………......96

xiii

LIST OF FIGURES

FIGURES Figure 2.1 Basic filament winding process .........................................................14

Figure 2.2 Polar winding .....................................................................................15

Figure 2.3 Helical winding ..................................................................................16

Figure 3.1 Internal pressure test tube ..................................................................30

Figure 3.2 Internal pressure test system...............................................................31

Figure 3.3 Schematic view of the pressure test system........................................31

Figure 3.4 Tube with the test fixtures...................................................................33

Figure 3.5 Three axial computer controlled Bolenz&Scafer filament winding

machine...............................................................................................35

Figure 3.6 Schematic view of the steel mandrel...................................................35

Figure 3.7 Curing furnaces...................................................................................39

Figure 3.8 Test tubes.............................................................................................40

Figure 3.9 Schematic representation of UFRA-5-350-23 strain gauge................41

Figure 3.10 Pressure recording system...................................................................43

Figure 3.11 Strain gauge data acquisition system..................................................44

Figure 4.1 Hoop stress – strain data for the carbon fiber reinforced of [±25°]3

[90°]1 winding angle configuration ....................................................49







Figure 4.5 Hoop stress – strain data for the carbon fiber reinforced of [90°]7

winding angle configuration ..............................................................53

xiv

Figure 4.6 Hoop stress – strain data for the glass fiber reinforced of [±25°]2 [90°]1

winding angle configuration ...............................................................56







Figure 4.10 Hoop stress – strain data for the glass fiber reinforced of [90°]5


Figure 5.1 Burst performance factors for the carbon fiber reinforced tubes

manufactured without extra tensioning ..............................................69

Figure 5.2 Burst performance factors for the carbon fiber reinforced tubes

manufactured with extra tensioning ...................................................69

Figure 5.3 Burst performance factors for the glass fiber reinforced tubes


Figure 5.4 Burst performance factors for the glass fiber reinforced tubes


Figure 5.5 Burst performance factors for the carbon fiber reinforced tubes .......72

Figure 5.6 Burst performance factors for the glass fiber reinforced tubes ..........72

Figure 5.7 Burst performance factors of the tubes without extra tensioning .......74

Figure 5.8 Burst performance factors of the tubes with extra tensioning ............74

Figure 5.9 Burst pressure performance factors ....................................................75

Figure 5.10 Hoop elastic constant for the carbon fiber reinforced tubes


Figure 5.11 Hoop elastic constant for the carbon fiber reinforced tubes


Figure 5.12 Hoop elastic constant for the glass fiber reinforced tubes manufactured

without extra tensioning .....................................................................77

Figure 5.13 Hoop elastic constant for the glass fiber reinforced tubes manufactured

with extra tensioning ..........................................................................78

xv

Figure 5.14 Hoop elastic constants for the carbon fiber reinforced tubes .............79

Figure 5.15 Hoop elastic constants for the glass fiber reinforced tubes ................80

Figure 5.16 Burst performance factors of the tubes without extra tensioning .......81

Figure 5.17 Burst performance factors of the tubes with extra tensioning.............82

Figure 5.18 Hoop elastic constants........................................................................83

Figure 5.19 Failed carbon fiber reinforced tube of [±25°]3 [90°]1 winding

configuration ......................................................................................85

Figure 5.20 Failed glass fiber reinforced tube of [±25°]2 [90°]1 winding

configuration .....................................................................................85


configuration ......................................................................................86


configuration ......................................................................................87


configuration ......................................................................................88


configuration ......................................................................................89


configuration ......................................................................................89

Figure 5.26 Failed glass fiber reinforced tube of [90°]5 winding

configuration......................................................................................90

xvi

CHAPTER I

INTRODUCTION Many of the modern industrial applications and technologies require materials with

superior properties that cannot be met by conventional monolithic materials, such as

metal alloys, ceramics, and polymers. Considering the principle of the combined

action, better properties can be obtained by combination of two or more distinct

materials. Accordingly, material property combinations have been, and yet being

extended by the development of the composite, which is a multiphase material that

exhibits a proportion of the properties of the forming phases so that a better

combination of properties is obtained. Composites may have different properties that

its constituents do not posses, such as impact resistance being high for HPPE

composites.

Composite materials have several advantages over traditional engineering materials,

which make them attractive for many industrial applications. Composite materials

have superior mechanical properties like high specific stiffness, high specific

strength, high fatigue strength, and good impact properties. They can easily act as

“smart” materials, that is, they can provide in-service monitoring or online process

monitoring with the help of embedded sensors. Unlike most metallic materials, they

may offer high corrosion and chemical resistance. Besides, composite materials

provide good dimensional stability and design flexibility, they are appropriate for

near-net-shape processing, which eliminate several machining operations and thus

reduces process cycle time and cost. Although composites could offer many

beneficial properties, they suffer from the following disadvantages: compared to

most of the traditional engineering materials, material cost of the composite materials

is high, their high-volume production methods limit the widespread use of

composites. A problem with polymer matrix composites is that they absorb serious

1

amounts of moisture, which, affects the mechanical properties and dimensional

stability of the components. The temperature resistance and solvent resistance

depend strongly on the matrix material.

Composite structures are employed in a wide range of industrial applications;

transportation, aerospace, automotive, construction, marine, military, electronics,

sports, civil engineering, etc. S.K. Mazumdar [1] reported the levels of composite

shipments up to 545 million kg for transportation industries, and 340 million kg for

construction industries in the USA for the year 2000. Also, composites have a great

share in the high technology industries such as aerospace, defense, electronics, etc,

up to shipment levels of 180 million kg.

Composites are also used in several design applications. Composites can be designed

for different types of (tensile, compressive, impact, internal, torsion, and possible

combinations of these) loading. For design purposes, it is vital to clarify the

mechanical responses of composites to the mentioned loading types. As a result,

studies are and being carried out to determine the mechanical behavior of composite

structures under different loading conditions.

1.1 Objective of the Study

The objective of the study is to assess the mechanical behavior of the filament wound

composite tubes working under internal pressure by experimental techniques to

develop a database for design of filament wound pressure vessels and determination

of their useful life cycle. To find these,

- Maximum hoop stresses formed during loading,

- Strains in hoop direction,

- Elastic constants in hoop direction,

2

will be determined, and thus the necessary data of to be used in the design

applications will be generated and identified.

To obtain this data, a proper gripping system, an internal liner and end

reinforcements are designed for the test tubes, and the test tubes are manufactured by

wet filament winding method. Internal pressure tests are applied on the test tubes

according to ASTM D 1599-99 standard, and the test results are evaluated and

compared with the data in literature.

Chapter 2 of the thesis will cover the theory of the composites; definitions,

classifications, materials used, production techniques and tests performed to identify

the mechanical properties and a brief literature review. Chapter 3 is on the

experimental work; test design, testing procedure, specimen geometry, materials

used and tube manufacturing. Chapter 4 describes the experimental results; burst test

and strain gauge data and their evaluation so that mechanical parameters are

identified and presented. Chapter 5 discusses the experimental results considering the

production variables; compare these results with the results obtained by different

mechanical testing methods and laminate analysis methods in literature. Chapter 6

concludes the study and gives possible future work.

3

CHAPTER II

THEORY AND LITERATURE REVIEW 2.1 Composites

Nature is full of examples where the idea of composites is present. The coconut palm

leaf, for example, is nothing but a cantilever using the concept of fiber

reinforcement. Wood is a fibrous composite: cellulose fibers in a lignin matrix. The

animal body is a composite of bone and tissue, where a bone itself is a natural

composite that supports the weight of various members of body. It consists of short

and soft collagen fibers embedded in a mineral matrix called apatite [2].

Strictly speaking, the idea of composite materials is not a new one. Ever since it was

recognized that combinations of different materials often resulted in superior

products, materials have been combined to produce composites. Mud bricks

reinforced with straw were known to have been made hundreds of years B.C., as

were laminated woods. Early history reports Mongol bows made from cattle tendons,

wood and silk bonded together with adhesives. Other examples include Japanese

ceremonial swords and Damascus gun barrels fabricated from iron and steel

laminates. In recent history, World War II can be considered to be a milestone for the

further development of composite technology. Nevertheless, the origin of a distinct

discipline of composite materials can safely be marked as the beginning of 1960s.

Since the early 1960s, there has been an ever increasing demand for materials ever

stiffer and stronger yet lighter in fields as diverse as space, aeronautics, energy, civil

construction, etc. The demands made on materials for better overall performance are

so great and diverse that no one material is able to satisfy them. This naturally led to

a resurgence of the ancient concept of combining different materials in an integral-

composite material to satisfy the user requirements. Such composite material systems

4

result in performance unattainable by the individual constituents and they offer a

great advantage of a flexible design [2,3].

At present, there is no universally accepted definition of the term “composite

material”. One definition might be “any material that consists of two or more

identifiable constituents” [3]. Such a definition could include almost everything

(excluding the single-phase, homogeneous materials); rocks, minerals, wood, animal

bones, etc. Even a metal can be considered to be a composite of many grains. In

order to avoid contra-version, an operational definition for composite should be

given, and that definition is as follows: A substance consisting of two or more

materials, insoluble in one another, which are combined to form a useful engineering

material possessing certain properties not possessed by the constituents, is called a

“composite material” [4].

Many composite materials are composed of just two phases; one is termed the

matrix, which is continuous and surrounds the other phase, often called the dispersed

phase or the reinforcement. The properties of composites are a function of the

properties of the constituent phases, their relative amounts, and the geometry (shape

of the particles, particle size, distribution and orientation) of the dispersed phase.

2.1.1 Classification of Composites

The composites may be classified according to their reinforcement types: particle

reinforced composites and fiber reinforced composites. But more commonly, the

classification is based on the matrix type: metal matrix composites (MMCs), ceramic

matrix composites (CMCs) and polymer matrix composites (PMCs).

2.1.1.1 Metal Matrix Composites

The MMCs are materials consisting of metal alloys reinforced with continuous

fibers, particulates or whiskers. The addition of these reinforcements gives MMCs

5

superior mechanical properties and unique physical characteristics. The two most

commonly used metal matrices are based on Aluminum and Titanium which both

have comparatively low specific gravities. Also, Beryllium, Magnesium, Nickel and

Cobalt based super alloys are can be used as matrix materials regarding the needs

and service conditions of the application. As reinforcement, generally SiC particles,

Boron and Al2O3 fibers, and Borsic (Boron fibers coated with SiC) and TiB2 coated

carbon fibers are employed. Because of their ability to provide the needed strength at

the lowest weight and least volume, MMCs are attractive for many structural and

nonstructural applications.

2.1.1.2 Ceramic Matrix Composites

CMCs in which ceramic or glass matrices are reinforced with continuous fibers,

whiskers, or particulates, mainly SiC and Si3N4, are rising as a type of advanced

engineering structural materials. Ceramics have very attractive properties for many

applications; high strength and stiffness at high temperatures, low density and

chemical inertness. But the one serious disadvantage of this class of material is that

their susceptibility to impact damage and catastrophic failure in presence of flaws.

CMCs has been to toughen the ceramic matrices by incorporating reinforcements in

them and thus obtain the attractive high temperature properties with drastically

decreasing the risk of sudden catastrophic failures.

2.1.1.3 Polymer Matrix Composites (PMCs)

The thesis is on PMCs. Therefore major emphasis will be given to this topic.

PMCs consist of a polymer matrix, either thermoset or thermoplastic, and fibers or

other materials with sufficient aspect ratio as the reinforcing medium, which, in

general, is glass, Carbon, Boron and Kevlar. The low weight of the matrix material is

accompanied by the attractive mechanical properties of the reinforcement. As a

result, a composite material with quite high specific mechanical properties is

6

obtained, accompanied with low cost and ease of fabrication, which is widely

employed in several application areas.

2.1.1.3.1 Matrix Materials

In polymer matrix composites, as in all composite materials, the matrix serves to

transfer stresses between the fibers, holds the reinforcement phase in place and

protects the surface of the fibers from mechanical abrasion. It has a minor role in

tensile load carrying capacity of the composite structure.

Polymers are particularly attractive as matrix materials due to their relatively easy

processibility, low density and good mechanical and dielectric properties. They are

divided into two broad categories: thermoplastics and thermosets. The thermoplastic

polymers can be heat-softened, melted and reshaped many times. In a thermoset

polymer, however, the cross links that form a rigid network of molecules cannot be

broken; thus the polymer cannot be melted or reshaped by application of heat and

pressure.

When combined with reinforcements, thermoplastic polymers offer unique

advantages. The most important advantages are lower cost of manufacturing,

accompanied with high impact strength and high fracture resistance. These attractive

mechanical properties result in a very good damage tolerant behavior in the

composite. Generally, compared to thermoset polymers, thermoplastics have higher

strains to failure, which shall provide better resistance to many mechanical damage

types, like matrix microcracking. The most common thermoplastic resins employed

in composite manufacturing and their common characteristics are as follows:

- Nylon, which has high toughness and impact resistance,

- Polyetheretherketone (PEEK), with excellent chemical and wear resistance,

- Polypropylene (PP), with high specific strength, low cost, very good chemical

resistance and ductility,

7

- Polyphenylene sulphide (PPS), with excellent balance in strength and high

temperature resistance at low cost,

- Polyimides (PAI), that have relatively high service temperature range.

Traditionally, thermoset polymers are employed in fiber reinforced composites. They

are an important source of properties, superior mechanical characteristics, and better

handling properties compared to thermoplastic resin systems. The most common

thermoset resins employed in the composite manufacturing and their common

characteristics are as follows:

- Unsaturated polyesters, with attractive mechanical, chemical and electrical

properties accompanied with dimensional stability, cost and ease of

processing and fast curing,

- Epoxies, with superior mechanical and electrical properties, resistance to

corrosive environments, good performance at elevated temperatures,

- Vinyl esters, which combine the superior mechanical properties of epoxy

resins with the handling advantages of the unsaturated polyester resins,

- Phenolics, with high performance characteristics like high temperature,

chemical and creep resistance,

- Polyurethans, with good impact resistance, and

- Bismaleimides (BMI), with high temperature resistance.

The mechanical properties of polymeric resin systems employed as matrix materials

are given in Table 2.1.

8

Table 2.1 Mechanical properties of resins [5].

Resin Type Density

(Mg/m3)

Modulus

(GPa)

Strength

(MPa)

THERMOPLASTIC

Nylon

PEEK 1.26 – 1.32 3.2 93

PP 0.9 1.1 – 1.6 31 – 42

PPS 1.36 3.3 84

PAI 1.4 3.7 – 4.8 93 – 147

THERMOSET

Polyester 1.1 – 1.23 3.1 – 4.6 50 – 75

Epoxy 1.1 – 1.2 2.6 – 3.8 60 – 85

Vinyl Ester 1.12 – 1.13 3.1 – 3.3 60 – 90

Phenolic 1.0 – 1.25 3.0 – 4.0 60 – 80

Polyurethan 1.2 0.7 30 – 40

Bismaleimides 1.2 – 1.32 3.2 – 5.0 48 – 110

2.1.1.3.2 Reinforcement Materials

Reinforcements for PMCs can be fibers, particles or whiskers. Each has its own

unique application, although fibers are the most common, and have the greatest

influence on properties. Fibers are the materials with very high aspect ratios; i.e. they

have one very long dimension compared to the others. They have significantly more

strength in the long direction than the other directions.

The most common fiber reinforcements for PMCs and their common characteristics

are as follows:

9

- Glass fibers with different special characteristics:

o E glass, with high electrical insulating properties,

o S glass, with high strength, heat resistance and modulus,

o S2 glass, with similar properties to S glass, but of lower cost,

o C glass, with high chemical corrosion resistance,

o A glass, with high alkali content and thus excellent chemical

resistance but lower electrical properties,

o D glass, with excellent electrical properties, but lower mechanical

properties.

- C (graphite) fiber, with very high strength and modulus, which remain

constant even at high temperatures,

- Metal fibers, high strength and resistance to high temperatures,

- Alumina fiber, with excellent resistance to high temperatures,

- Boron fiber, with high modulus and excellent resistance to buckling,

- Polymeric fibers, mainly Aramid, with high strength and modulus.

The mechanical properties of the fibers employed as reinforcement in PMCs are

given in Table 2.2.

10

Table 2.2 Mechanical properties of commercial fibers [6].

Fiber Type Density

(Mg/m3)

Tensile

Modulus

(GPa)

Tensile

Strength

(GPa)

Specific

Modulus

(m*105)

Specific

Strength

(m*105)

GLASS & QUARTZ

E Glass 2.54 69 2.4 27 0.9

S Glass

(Owens

Corning)

2.55 86 3.45 34 1.4

Quartz

(Quartz&

Silica)

2.2

69

3.69

31

1.7

ARAMID

Kevlar 149 1.47 179 3.45 122 2.3

Twaron HM 1.45 121 3.15 83 2.2

Kevlar 29 1.44 58 3.62 40 2.5

CARBON

UHM

(Thornel P-

120S)

2.18 827 2.2 379 1.0

UHM

(Celion GY-

80)

2.18 572 1.86 291 0.9

UM

(Microfil

55)

1.83 379 3.45 207 1.9

IM

(Magnamite

IM 8)

1.8 303 5.3 168 2.9

SM

(Torayca

T300)

1.75 230 3.53 131 2.0

11

Table 2.2 (continued)

Fiber Type Density

(Mg/m3)

Tensile

Modulus

(GPa)

Tensile

Strength

(GPa)

Specific

Modulus

(m*105)

Specific

Strength

(m*105)

LM (Kureha

T101 F) 1.65 33 0.79 20 0.5

CERAMIC

Silicon

carbide

(Nicalon)

2.55 193 2.76 76 1.1

Alumina-

Silicate

(Saffil)

3.3 300 2.0 91 0.6

Silicon-

Titanium

(Tyranno)

2.35 206 2.74 87 1.2

Boron 2.57 400 3.6 156 1.4

METAL

Stainless

Steel Fiber 7.9 197 1.45 25 0.2

Steel, Piano

Wire 7.8 207 2.41 26 0.3

2.1.1.3.3. Manufacturing Methods

To fabricate continuous fiber-reinforced PMCs, the very important point is that the

fibers should be oriented all in the same direction and should be distributed

uniformly throughout the plastic matrix. Various techniques are used for the

manufacturing of PMCs. The most common techniques are as follows:

12

- Hand Lay-Up and Spray-Up

- Sheet Molding Compound

- Bulk Molding Compound

- Autoclave

- Resin Transfer Molding

- Pultrusion

- Filament Winding

- Injection Molding

- Automated Tape Placement

Of these, filament winding is a very important and widely used technique for PMC

production and is used for the present investigation.

Filament Winding

Filament winding is a process where the continuous fibers are accurately positioned

in a prearranged pattern to form a cylindrical shape. Figure 2.1 shows a basic

filament winding process. A number of fiber rovings are pulled from a series of

creels and tensioners that control the tension of the fibers into a liquid resin bath that

contains the resin itself, the hardeners and the accelerators. At the end of the resin

tank, the rovings are pulled through a wiping device where the excess resin is

removed from the rovings. Once the rovings are thoroughly impregnated and wiped,

they are collected together in a flat band, pass through the carriage and located on the

mandrel. The traversing speed of carriage and the winding speed of the mandrel are

controlled to generate the desired winding angle patterns. After the appropriate

number of layers has been applied, curing is carried out in an oven or at room

temperature, after which the mandrel is removed [2].

13

Figure 2.1 Basic filament winding process [7].

The filament winding method in general, has several advantages over other methods.

The foremost advantages can be listed as:

- It is highly repetitive and precise in fiber placement.

- It can use continuous fibers to cover the whole component area, which

simplifies the fabrication process of many components and increases

reliability and lowers the cost by reducing the number of joints.

- It is less labor intensive, which reduces the costs significantly.

- Large and thick walled structures can be built.

The cons of the method may be listed as follows:

- The shape of the component must be chosen in a way that it can be removed

from the mandrel.

- Generally, reverse curvatures cannot be wound.

14

- The mandrel used generally is complex and expensive.

- Surface quality is low.

The filament winding process can be classified as polar and helical winding. In polar

winding, delivery head travels around a slowly indexing mandrel, whereas in helical

winding, fiber is fed from a horizontally translating delivery head to the rotating

mandrel.

Polar Winding: In polar winding, the carriage rotates around the longitudinal axis of

a stationary (but indexable) mandrel. After each rotation of the carriage, the mandrel

is indexed to advance one fiber bandwidth, so that the fiber bands lie adjacent to each

other and there are no crossovers. A complete wrap consists of two plies oriented at

plus and minus the wind angle on the two sides of the mandrel. In contrast with

helical winding, polar windings are employed with lower wind angles. Figure 2.2

shows polar winding.

Figure 2.2 Polar winding [7].

15

Helical Winding: This type of winding requires a system capable of laying down a

band in helical patch over the surface of the turning mandrel, turning it around on the

end, and returning to the starting position to repeat the cycle. The angle of roving

band with respect to the mandrel axis is called the wind angle [7]. By adjusting the

speed of the carriage and the rotational speed of the mandrel, any wind angle

between 0o and near 90o can be obtained. The mechanical properties of the

composites that are wound helically strongly depend on the wind angle. Besides

being the predominant filament winding method, there are a number of limitations to

helical winding, which include the machine bed size, mandrel weight and turning

diameter clearances. Figure 2.3 shows helical winding.

Figure 2.3 Helical winding [7].

Hoop (Circumferential) Winding: In hoop winding, which is a specialized helical

winding technique, bands are wound almost perpendicular to the mandrel axis, that

is, the winding angle approaches to 90o. In production, hoop windings are generally

associated with other wind angles as they provide a significant reinforcement in hoop

direction.

16

2.2. Mechanical Characterization of Filament Wound Tubes

lications. Based on this fact, several tests are

erformed on composite structures.

.2.1 Test Methods and Their Standards

efined

onditions of pretreatment, temperature, humidity and test machine speed [8].

etermine the compliance

of the component with the minimum burst requirements [9].

to pipe in which the ratio of outside diameter to wall thickness

is 10:1 or more [10].

It is essential to know the mechanical characteristics of filament wound tubes in

order to employ them in design app

p

2

The one most common testing method is the split ring test. The test is done according

to ASTM D2290-04, to determine the apparent hoop tensile strength. The test is

mainly for most of the plastic products utilizing a split disk test fixture under d

c

In order to determine the hydraulic pressure that produces failure of either

thermoplastic or reinforced thermosetting resin pipe, tubing, or fittings in a short

time period, tests according to ASTM D1599 is employed. This test method is used

for determination of the resistance of either thermoplastic or reinforced thermosetting

resin pipe, tubing, or fittings under hydraulic pressure for short time periods. The

standard gives two procedures; Procedure A is used to determine burst pressure if the

mode of failure is to be determined. Procedure B is used to d

Cyclic pressure tests are done according to ASTM D2143-00 Standard, titled as

“Test Method for Cyclic Pressure Strength of Reinforced, Thermosetting Plastic

Pipe”. The standard describes the methods for the determination of the failure

characteristics of reinforced plastic pipe when subjected to cyclic internal hydraulic

pressure. It is limited

The standard ASTM D2992-01, “Standard Practice for Obtaining Hydrostatic or

Pressure Design Basis for Fiberglass (Glass-Fiber-Reinforced Thermosetting-Resin)

Pipe and Fittings” is another standardized test method that is employed in the

17

determination of mechanical properties of polymer matrix composites. The practice

given in the standard is for two procedures, namely Procedure A (cyclic) and

Procedure B (static) loading. It is used for obtaining a hydrostatic design basis for

fiberglass piping products, by evaluating strength-regression data derived from

testing pipe or fittings, or both, of same materials and construction, either separately

or in assemblies. The standard is also applicable for both glass-fiber-reinforced

ermosetting-resin pipe and glass-fiber-reinforced polymer mortar pipe [11].

-fiber-reinforced

olymer mortar pipe (RPMP) are classified as fiberglass pipes [12].

to-failure of plastic piping products under

onstant internal pressure and flow [13].

th

In order to determine the tensile properties of the filament wound composite tubes,

ASTM standard D2105-01 (Standard Test Method for Longitudinal Tensile

Properties of Fiberglass (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe and

Tube) is used. The method discussed in the standard covers the determination of the

comparative longitudinal tensile properties of fiberglass pipe when tested under

defined conditions of pretreatment, temperature, and testing machine speed. Both

glass-fiber-reinforced thermosetting-resin pipe (RTRP) and glass

p

Another important property, creep life for the filament wound tubes can be

determined experimentally according to the ASTM standard F948-94(2001)e1, titled

“Standard Test Method for Time-to-Failure of Plastic Piping Systems and

Components Under Constant Internal Pressure With Flow”. This test method

discusses the determination of the time-

c

The compressive properties of the polymer matrix composites are determined

according to the ASTM standard D3410/D3410M-03; “Standard Test Method for

Compressive Properties of Polymer Matrix Composite Materials with Unsupported

Gage Section by Shear Loading”. The standard describes the in-plane compressive

properties of polymer matrix composite materials reinforced by high-modulus fibers.

The composite material forms are limited to continuous-fiber or discontinuous-fiber

reinforced composites for which the elastic properties are specially orthotropic with

18

respect to the test direction. The test procedure introduces the compressive force into

the specimen through shear at wedge grip interfaces. This type of force transfer

differs from the procedure in Test Method ASTM D695 where compressive force is

ansmitted into the specimen by end loading [14].

-plane loading where the loading is defined in terms

f a test control parameter [15].

ent of +45° laminate, capable of being tension tested in

e laminate direction [16].

iterature Survey on Mechanical Characterization of Filament Wound

ubes

tr

A very important property, fatigue properties of the polymer matrix composites can

be evaluated employing the ASTM standard D3479/D3479M-96(2002)e1, titled

“Standard Test Method for Tension-Tension Fatigue of Polymer Matrix Composite

Materials”, within the scope of determination of the fatigue behavior of polymer

matrix composite materials subjected to tensile cyclic loading. The composite

material forms are limited to continuous-fiber or discontinuous-fiber reinforced

composites for which the elastic properties are especially orthotropic with respect to

the test direction. The test method discusses the unnotched test specimens subjected

to constant amplitude uniaxial in

o

For determination of the shear properties of the polymer matrix composites, tests

according to the ASTM D3518/D3518M-94(2001) standard can be employed. The

standard is titled as “Standard Test Method for In-Plane Shear Response of Polymer

Matrix Composite Materials by Tensile Test of a ±45o Laminate”, and the test is

developed for the determination of the in-plane shear response of polymer matrix

composite materials reinforced by high-modulus fibers. The composite is limited to a

continuous-fiber reinforcem

th

2.2.2 L

T

Considering the importance of knowing the mechanical characteristics of filament

wound tubes in applications, there is a considerable amount of work carried out in

literature on this subject. In most of the studies, mechanical constants and

19

characteristics are determined by means of several mechanical tests and analytical

studies. P. Mertiny, F. Ellyin, and A. Hothan studied the effect of multi axial

filament winding on tubular structures of three different winding configurations by

comparing the data of [±45, ±602] and [±30, ±602] with [±603], so called baseline

data, under constant ratios of biaxial loads [17]. In this work, two types of failures

are distinguished; functional failure, where leakage of test fluid takes place but the

structure still carries load, and structural failure, where the specimen can no longer

carry any load. The writers evaluated the experimental hoop and axial stresses at

both functional and structural failure, derived the elastic constants for pure hoop and

axial loading conditions and studied the failure envelopes. It was concluded that the

failure modes depend strongly on applied stress ratio, and matrix damage can be

minimized using [±30, ±602] configuration. [±45, ±602] and [±30, ±602]

configurations showed higher functional and structural strength compared to the

baseline configuration under hoop-to-axial load ratios smaller than 1, due to the

reduced axial strain in ±60 covers; whereas the baseline configuration performed best

under pure hoop loading condition. Multi angle winding configurations exhibit

improved strength especially in [2H:1A] loading condition, which is often the case in

bular pressure vessels. tu

Another study performed to obtain experimental data that represents the effect of

winding angle on the mechanical properties of filament wound composites that are

subjected to uniaxial and biaxial stresses is carried out by P. D. Soden et. al [18].

Biaxial loading (hoop and axial loadings) for lined and unlined specimens at

different winding angles and uniaxial compression is applied to tubular specimens.

Electrical resistance strain gages are attached to some of the specimens during testing

and the data obtained are evaluated to determine elastic constants. Accordingly,

stress-strain curves are plotted using the strain data from the strain gages and the

axial stress and hoop stress data evaluated from the burst tests. The data obtained are

compared with the results of relevant studies and conclusions are made considering

all the literature and experimental data. The work also discusses the variation of the

failure stresses at different tests, effect of the wall thickness on the compressive

20

properties, effect of stress concentrations through the gauge length and compares the

stress envelopes in the work and literature for different winding angles. It was

concluded that the test specimens without internal liners could withstand lower loads

due to the leaking at the matrix cracks. The leakage and fracture strengths are

affected considerably with winding angles while winding angle has a slight effect on

axial compression strength. Larger winding angles increases the tube’s uniaxial

tensile strength in the hoop direction whereas decreases uniaxial tensile strength in

axial direction. Also, the stress-strain analysis showed that elastic constants vary with

winding angle as expected from laminate theory. Another study performed by the

writers discussed the experimental failure stresses for ±55° filament wound glass

fiber reinforced plastic tubes under biaxial loads [19]. For that, axial loads are

applied, accompanied with the internal pressure, and the applied circumferential

stress to axial stress ratio is kept constant throughout the tests. ±55° filament wound

tubes are tested under different stress ratios and the failure test results are recorded.

The work described the first stage and final failure modes of the ±55° specimens and

the theoretical stress distributions; and discussed the effects of stress distribution on

strength, the scatters in failure stresses, and compared them with the previous results.

It is stated that when applied hoop stresses are low, the strength of the tube is

reduced considerably. The uniaxial compressive strength is almost twice the uniaxial

tensile strength but the axial compressive strength is reduced by the presence of high

circumferential stresses, unlike the axial tensile strength. For uniaxial tension and

compression, there was no evident difference between the initial and final failure

stresses. Also, it is shown that the maximum hoop strength occurred between the

circumferential to axial stress ratios of 3:1 and 3.5:1 whereas the maximum axial

trength occurred at a circumferential to axial stress ratio of 2:1. s

F. Ellyin, M. Carroll, D. Kujawski and A.S. Chiu studied the behavior of

multidirectional filament wound glass fiber/epoxy tubular structures under biaxial

loading [20]. The study aims to investigate the effects of the rate and ratio of biaxial

loading on failure strength, damage accumulation and monotonic stress - strain

behavior of glass fiber reinforced epoxy tubes. To do that, different hoop to axial

21

stress ratios are employed in testing; failures are studied and biaxial failure envelopes

of stress and strain are developed and interpreted. It was concluded that strength and

stiffness are functions of biaxial stresses, failure modes and damage accumulations at

failure are dependent on biaxial stress ratio, and linear elastic behavior of the tubes

an only be observed at relatively low temperatures.

stress levels, there is much more cycles in between leakage and final

failure stages.

c

In the study of N. Tarakçioğlu, L. Gemi and A. Yapıcı, the fatigue behavior of glass

fiber reinforced ±55° filament wound composite tubes is investigated experimentally

[21]. The specimens produced from E-glass fiber with epoxy resin are tested at an

open ended internal pressure apparatus and the fatigue tests are performed according

to the ASTM standard D2992. In the study, six different stress levels based on

different percentages of the static strength of the specimen were applied at one

frequency. During testing, three damage mechanisms are observed. These

mechanisms are identified as crazing, leakage and final failure; and the number of

cycles to these predetermined levels are investigated and recorded. In addition, S-N

curves are drawn for each damage stage. In the study, it was shown that there is an

analogy between macro and micro damage stages of the specimens. In addition, at

higher stress levels, the final failure of the specimen occur just after the leakage

whereas for low

A. S. Kaddour, M. J. Hintonand P. D. Soden studied experimentally the behaviour of

±45° glass/epoxy filament wound composite tubes under quasi-static equal biaxial

tension–compression loading [22]. Test are performed on ±45° tubes under 1:−1

stress ratio, unidirectional lamina (circumferentially-wound tubes) under torsion,

±45° angle ply filament wound tubes under uniaxial tension and ±45° angle ply

filament wound under stress ratio SR=2.3:−1. The writers gave the necessary

equations describing the unidirectional shear stress and strain values obtained from

tests on tubes under various loadings conditions first, and then considering the

experimental results, they obtained the pressure, load and stress-strain curves and

examined failure appearances. Considering this data, comparison is made between

22

the shear stress–strain curves extracted from tests and the work discussed the factors

affecting the behaviour of specimens under biaxial loadings: buckling of specimens,

effects of bulging, effects of scissoring, effects of thermal stresses, effects of

transverse stress component and effects of micro cracking.

he matrix cracking, where internal pressure governed the amount of

delamination.

Biaxial fatigue behavior of a multidirectional filament-wound glass fiber/epoxy pipe

is studied by F. Ellyin and M. Martens [23]. In their study, the writers aimed to

investigate the fatigue life and leakage behavior of a multidirectional filament

wound, glass fiber reinforced epoxy tube by determining the deformation behavior of

the pipe under different applied biaxial stress ratios, leakage curves and leakage

envelopes for each applied stress ratio, and micro and macro failure modes by

physical observation and measured parameters. The test specimen configuration was

[±664, 0, ±663, 0, ±663, 0, ±665 ]. It was shown from the biaxial fatigue tests that the

decrease in secant modulus with cyclic loading and the leakage are strongly

dependent on both the applied maximum biaxial stress and the applied biaxial stress

ratio. Also, in all cases of loading, there was a significant decrease in the secant

modulus which stabilizes after a certain period and this reduction indicates that

indicate that there is a relation between the stress ratio and the maximum applied

stress and the largest initial reduction was observed in the axial secant modulus under

pure axial loading and in the hoop secant modulus under pressure vessel type loading

(2.5H:1A). Another consequence of the results is that the damage, which ranged

from a uniform matrix cracking to a delamination with pinhole bursting or a

combination of both, is dependent on the maximum applied stress. The observed

damage indicated that the amount of axial tension in the specimen governs the

uniformity of t

Another study, carried out by C. Kaynak and O. Mat, discussed the effect of stress

level and loading frequency on the fatigue behavior of filament wound composite

tubes [24]. In their work, tensile tests were applied to the tubular test specimens and

the number of cycles to three predetermined fatigue damage stages (crazing in the

matrix, crazing along the fiber winding direction leading to debonding, and fiber

23

breakage and total failure) were monitored as a function of test frequency and stress

level. In the study, it was shown that fatigue resistance of the composite tubes

decreased considerably when the stress level was increased and life increases as the

ading frequency was raised.

igh fiber

olume fraction, the microcracks propagated at the fiber/matrix interfaces.

l work showed that these

inforcements should be principally in the bore section.

lo

J. Bai, P. Seeleuthner, and P. Bompard studied in detail the mechanical behavior of

±55° filament wound glass fiber/epoxy resin tubes [25]. The tube was made of six

plies of ±55° winding angle. A series of mechanical tests were performed under

different loading conditions; pure tensile loading, pure internal pressure and

combined loading. The work discussed the damage mechanisms under these

conditions. It is stated that the damage and failure process can be described by three

steps: initiation of the damage process by microcracking, delamination between the

different plies, and development and coalescence of cracks and delaminations in

different plies. Also, it is confirmed that at that zones free of fibers, matrix cracks

occur perpendicular to the tensile direction, at the zones where fiber volume fraction

is low, microcracks propagated around fiber bundles, and at the zones of h

v

M.R. Etemad, E. Pask and C.B. Besant described an experimental and computational

work to determine the hoop strength and other mechanical properties like tensile

modulus, tensile strength and Poisson’s ratio of two carbon fiber reinforced

composite in their work [26]. Experimental results showed that hoop winding should

be reinforced with axial winding, where computationa

re

In literature, the mechanical characteristic of filament wound pressure vessels are not

only studied by experimental work, but analytical procedures, numerical solutions

and finite element analysis are commonly employed in characterization. L. Parnas

and N. Katırcı analyzed the cylindrical pressure vessels by thin wall and thick wall

solutions [27]. They developed an analytical procedure for the design and prediction

of behavior of fiber-reinforced composite pressure vessels under combined

24

mechanical and hygrothermal loading. The writers employed the classical lamination

theory and generalized plane strain model in the formulation of the elasticity

problem. A cylindrical shell having a number of sub-layers, which are cylindrically

orthotropic, is regarded as in the state of plane strain. Loads applied are internal

pressure, body force due to rotation, axial force with temperature and moisture

variation. In the study, it was concluded that the optimum winding angle for filament

wound composite tubes that are subjected to internal loading is 52.1° and 54.2°,

which is consistent with the data present in literature. In addition, it was stated that

the burst pressure value depends on the analysis method used and thin-wall analysis

said to be an average, but a safe choice.

e benefits of

wind angle variation are more considerable under the last ply criterion.

is

P.M. Wild and G.W. Vickers studied the analysis of filament wound cylindrical

shells under combined centrifugal, pressure and axial loading [28]. The writers

developed an analytical procedure to asses the stresses and deformations of filament

wound structures under different loading types. The procedure developed is mainly

based on classical laminated plate theory, and models both plane stress and plain

strain states of a cylindrical shell having a number of sub-layers, which are

cylindrically orthotropic. It is concluded that when there is no axial loading, benefit

of wind angle variation is more significant. If axial loads are present, th

J.-S Park, C.-S. Hong, C.-G. Kim and C.-U. Kim studied the analysis of filament

wound composite structures considering the change of winding angles through the

thickness direction [29]. The test specimens are filament wound composite cylinders,

but closed at the ends by means of domes. The behavior of the filament wound

structure subject to internal pressure was analyzed considering the winding angle

change through the thickness. The writers employed finite element analyses

considering the change of winding angles through the thickness under internal

pressure loads, by a commercial finite element analysis code, ABAQUS and coded a

user subroutine to impose the change of winding angles to each solid element. They

also performed internal pressure tests and worked to verify the finite element

25

analysis results considering geometrical nonlinearities with the experimental data,

and it was shown that the experimental results showed good agreement with the

analysis results. It was concluded that it is required to consider the winding angle

change through the thickness direction for the precise prediction of stress distribution

over the domes and near the openings in order to not to have the undesirable failures.

ing angles and loading conditions are discussed and

ilure envelopes are obtained.

the

ipe studied changes from positive to negative with respect to the winding angle.

C. Gargiulo, M. Marchetti, and A. Rizzo studied on the prediction of failure

envelopes of composite tubes, which are subjected to biaxial loadings [30]. The

writers worked to provide numerical and experimental data on the strength of carbon

fiber reinforced epoxy filament wound tubes. The effects of winding angle on the

failure loads are investigated. For that, variety of combinations of internal, external

and axial loads are applied on the tests specimens to produce biaxial stress states and

test results are examined. Finite element method is also employed and the results of

experiments are compared with finite element results. Different damage and failure

mechanisms for different wind

fa

Another study that is performed by M. Xia, K. Kemmochi and H. Takayanagi,

discusses the analysis of filament-wound fiber-reinforced sandwich pipes [31]. The

work analyzes the stresses and strains of a filament-wound sandwich pipe subjected

to internal pressure and thermo-mechanical loading, based on the classical laminated

plate theory in detail, and give the numerical results and discussions. It is concluded

that netting analysis can be employed for the design of the optimum winding angle,

which depends upon geometry and construction materials and also, for a thick-walled

laminate-ply sandwich pipe, a 55° winding angle is no longer an ideal arrangement.

In addition, it was stated that, under internal pressure loads, the axial strain of

p

X.-K. Sun, S.-Y. Du, and G.-D Wang discussed the bursting problem of filament

wound composite pressure vessels by using nonlinear finite element method [32]. By

this method, the writers calculated the stresses and the bursting pressure of filament

26

wound composite pressure vessels. During failure analysis, maximum stress failure

criteria and stiffness-degradation model are employed. It was concluded that the

design method from the equivalent case to its real one is not sensible. To obtain the

ptimum structure, all affecting factors should be considered in detail.

used in health monitoring

vestigations and life studies based on these methods.

o

The above summary shows that there is source of information on the performance of

internally pressurized composite tubes. Most applications require the estimation of

life cycle performance of these composite tubes. This work is the first step to

generate data for a future work that would be

in

27

CHAPTER III

EXPERIMENTAL WORK

This chapter will cover the experimental work carried out; the test specimens and

testing procedure in detail. Test specimen design, manufacturing and nomenclature,

strain measurements, testing procedure and reporting will be discussed.

3.1 Test Tube (Specimen) Design

Internal pressure tests are extensively employed in mechanical characterization of

composite tubes. The method generates stresses in the material, primarily in the hoop

direction, and provides important information on the mechanical properties of the

tubes that are subjected internal pressure.

As discussed in several scientific works and commercial standards, to obtain reliable

data, the test should be carried out within some predefined constraints, which will be

discussed in the next paragraphs. These constraints are taken into consideration for

the test specimen design, and the design is optimized by improving some details.

One important point that should be considered is that, during internal pressure

testing, stress concentration arises around the end closure grips. This phenomenon

may lead the specimen failing at the stress concentrated region in a non-

homogeneous way, which surely affects the test results and reliability of the data, in

view of not obtaining the expected fracture type. For the design of an effective

internal pressure test specimen, it should be guaranteed that uniform stresses are

obtained through the test section and that failure takes place within the gauge length.

To assure this, specimen end reinforcements that reduce the stress concentration

effect around the end closures are employed in the tests. A straight reinforcement

28

would cause a similar stress concentration effect at the points where it ends, and

accordingly the reinforcements are designed in a stepped manner, where the wall

thickness gradually decreases with distance through the specimen length, at both

ends and at some point, homogenizes with the gauge length, that is, the specimen

wall thickness.

Another point is that the failures in the tests are expected to be catastrophic, that is,

bursting is desired, and any condition that shall not permit that, should be prevented.

However, leakage at the matrix cracks during internal pressure loading, and not

being able to obtain catastrophic failure is a serious problem that is encountered in

internal pressure tests of composite materials. To avoid the possible leakage of test

fluid; thus an unwanted failure mode, an elastomeric liner is placed in the specimen.

During loading, the internal liner is filled with the test fluid and pressurized. The

liner, whose load carrying capacity is neglected in the work, also helps preventing

the leakage of test fluid through the end gripping units during loading.

Another modification that is done is the reinforcement of all specimens with a single

layer of hoop winding as the outermost layer. This revision is considered when it was

observed that other winding angles result in quite irregular and rough surfaces, which

affects the test results. Application of a single layer of 90° reinforcement winding

would not only give rise to a much smoother outer surface, but also decreases the

possibility of fluid leakage in the cases where an internal liner is absent in internal

pressure loadings. Hoop layers contribute to the strength of the total tube. Indeed;

such hoop reinforcement layers are present nearly in all pressure vessel applications

as the outermost layer.

The test specimens are hollow, open-ended cylindrical tubes. They are of 400 mm

total length, and have an internal diameter of 60 mm, which is the outer diameter of

the mandrel employed in filament winding operation. The gauge length, which is the

length between the reinforcements employed, is 200 mm. The wall thicknesses

29

depend on the process parameters like tensioning condition and winding angle, and

the type of reinforcement. The geometry of the test specimen is given in Figure 3.1.

Figure 3.1 Internal pressure test tube.

3.2 Test Setup

Internal pressure tests are performed according to ASTM D 1599-99 standard. The

setup is composed of pressurizing system, test fixtures, strain gauge data acquisition

components and pressure recording units.

3.2.1 Pressure Test Setup

The internal pressure is applied by a micro-processor controlled 2000 Bar hydraulic

testing machine at the test facilities of BARIŞ Electrical Industries. The system

records the change in internal pressure with time during the test, until the specimen

fails, and so the bursting pressure. The system is accredited by METU Mechanical

Engineering Department. The pressure test system is given in Figure 3.2 and the

schematic view of the system is given in Figure 3.3.

30

Figure 3.2 Internal pressure test system.

Figure 3.3 Schematic view of the pressure test system.

31

OIL RESERVOIR

HIGH PRESSURE UNIT

TEST SPECIMEN VALVE HYDRAULIC PUMP

UNIT 150 bar

3.2.2 Test Fixtures

For the application of internal pressure efficiently, the specimen should be fixed

properly to the test apparatus. The fixing should be strong enough to avoid leakage of

test fluid, fracture or slip of the specimen at the matching region.

ASTM D 1599-99 standard offers two types of end conditions for internal pressure

testing: fixed end condition where the expansion in axial direction is hindered by

fixing the ends to each other, and open end condition, where there is no constraint on

the test specimen in axial direction.

The first system design was a fixed end gripping system that fixes the test specimen

at both ends, and thus restricts the motion in longitudinal direction. This was attained

by matching the two end units by means of metal bars. The system effectively

gripped the test specimens, but during loading, it was noticed that the specimen

expands considerably at the middle part in hoop direction and touches the metal bars

that are used for fixing the end closures to each other. This resulted in a significant

stress concentration at those points and a consequent early failure of the specimens.

Later the design has been changed, where one end of the test specimen is fixed to the

test unit, while it goes free on the other. This allowed the specimen expansion in the

longitudinal direction freely and eliminated the former significant swelling and

consequent early failure problem. Another point that is considered in employing this

design is that in open end condition, the hoop to axial stress ratio is 2:1, which is the

case in pressure vessels, and thus it simulates the pressure vessel better. Accordingly,

the tubes are fixed to the test system by means of the latter gripping end closure unit

for this test, which is presented in Figure 3.4.

32

Figure 3.4 Tube with the test fixtures.

3.2.3 Strain Gauge Data Acquisition System

The strain gauge data acquisition software is an 8 channel add-on card product of

PC-LabCards. The software uses Equation (3.1) for measurements.

0εkRR=

∆ (3.1)

where

∆R = resistance variation,

R = gauge resistance,

k = gauge factor,

εo = strain.

33

The software lets the user to adjust the record speed and the bridge voltage value.

Gauge resistance R and gauge factor k are identified and set by the user, and ∆R, the

variation in resistance is measured. In the hardware, there lies a dummy strain gauge,

and the system measures the difference of the resistances of the dummy strain gauge

and the actual strain gauge, ∆R. The software then evaluates the data and gives the

strain, εo as the output.

3.3 Specimen Manufacturing

The tubes that are employed in internal pressure tests are manufactured by utilizing

the filament winding technique, in the production facilities of BARIŞ Electrical

Industries.

3.3.1 Filament Winding Machine

The tubes are manufactured at a three axial computer controlled Bolenz & Schafer

wet filament winding machine. Maximum winding diameter of the machine is 500

mm and the maximum winding length is 4500 mm. The system is capable of utilizing

winding angles from 0° to 90° and its carriage receives the fibers from four creels.

The winding speed of the system is maximum 60m/min and it can carry a mandrel of

maximum 1000 kg. during the winding process, the system controls the fiber tension

and the temperature of the resin bath, up to 100°C. The filament winding machine is

given in Figure 3.5.

34

Figure 3.5 Three axial computer controlled Bolenz&Scafer filament winding

machine.

3.3.2 Tooling

Filament winding operation is performed on a 60 mm diameter steel mandrel. The

total length of the mandrel is 243 mm, and the winding length is 196 mm. The net

length, which gives the length of the tubes manufactured, is 160 mm. Figure 3.6

gives the schematic view of the mandrel.

Figure 3.6 Schematic view of the steel mandrel.

35

3.3.3 Filament Winding

Test tubes are manufactured by using an epoxy resin system with two different fiber

types, where, for each type, five different helical winding angles are used. As a

process parameter, extra tensioning is applied to fibers for some of the tubes during

manufacturing in order to observe the effect of wetting. The properties of the resin

system and the reinforcements employed in are as follows:

Resin System

The resin system employed in the fabrication of the tubes is CIBA Araldite MY740

(100 parts by weight) – Hardener HY918 (85 parts by weight) – Accelerator DY062

(0.2 – 2.5 parts by weight) mixture; a hot curing, low-viscosity impregnating resin

system. The system is characterized by its good mechanical and dielectric properties

and good aging resistance and is suitable for filament winding, wet laminating, and

pultrusion processes. The properties of the system are given in Table 3.1.

Table 3.1 Mechanical properties of the resin system employed.

Property Unit

MY740 – HY918 –

DY062

RESIN SYSTEM

Glass Transition Temperature (C) 123

Max. Tensile Stress (MPa) 61

Elongation At Break (%) 2

Elastic Modulus (MPa) 3637

36

Reinforcements

The reinforcements employed in the fabrication of the tubes are PPG Roving 1084

2400 TEX glass fiber; continuous product of PPG Industries, and Grafil 800 TEX

carbon fiber, continuous product of TOHO-TENAX. The properties of the

reinforcements are given in Table 3.2.

Table 3.2 Mechanical properties of the reinforcements employed.

Property Unit GRAFIL 800 TEX

CARBON FIBER

PPG 2400 TEX

GLASS FIBER

Max. Tensile Stress (MPa) 4900 2600

Elongation At

Break (%) 2 4 – 5

Elastic Modulus (MPa) 240000 73000

During the manufacturing of the test tubes, five different winding angles are

employed; 25°, 45°, 54°, 65°, 90°. To increase the strength of the tubes in hoop

direction and have a smooth surface, one hoop layer is wound on each of them, as

discussed in the previous sections.

Tensioning is applied to the fibers while they are pulled from the creels, in order to

get a better wetting of fibers by the resin. In the study, tensioning is used as a

parameter to observe the effect of wetting on mechanical properties. Accordingly, for

both fiber types, five different winding angles and two fiber tensioning levels, tubes

are tested. Extra tensioning is applied in a way that, weights of 1.5 kg each are hung

on four creels that supply the continuous fibers to the resin bath and then the winding

unit during fabrication. The tension values measured are given in Table 3.3.

37

Table 3.3 Measured tension values for the fibers.

Fiber Type Number of

Fiber Bands

Measurement

Location

Extra Weight

(kg)

Tension Value

carbon 1 creel 1.5 kg 1100 cN

carbon 2 creel 1.5 kg (x2) 2350 cN

carbon 1 creel - 800 cN



glass 4 resin bath - 49.3 kg

glass 4 resin bath 1.5 kg (x4) -

glass 2 resin bath 1.5 kg (x2) 45.2 kg

glass 2 resin bath 1.5 kg (x2) -

glass 2 resin bath - 5100-5200 cN

glass 1 resin bath - 2700 cN

glass 1 resin bath 1.5 kg 3500 cN

After the winding operation, the tubes are placed in the furnaces which are given in

Figure 3.7 for curing. Curing operation is carried out at 80°C for two hours, and then

at 120°C for another two hours. Once the curing is completed, the mandrel is

removed from the tubes and the composite hollow tubes are handled.

38

Figure 3.7 Curing furnaces.

To sum up, considering these production parameters, twenty tubes are fabricated by

employing two different reinforcement types, two different tensioning conditions and

five different winding angles.

3.3.4 Cutting the Tubes and Grinding of End Reinforcements

Once the tubes are manufactured and cured, they are then cut into the desired length

by means of mechanical cutting, each tube to give three test tubes. To have good fit

in the test fixtures, the reinforcement regions are grinded.

Test tubes are given in Figure 3.8.

39

Figure 3.8 Test tubes.

3.4 Tube Nomenclature

Considering the manufacturing parameters, a designation system is developed for the

tests. This system identifies the test tubes by the fiber type, winding angle, the

tensioning condition, and the position in the full length tube. The fiber type is

designated by the letter “E” followed by the numbers 1 or 2, which are assigned to

carbon fiber and glass fiber, respectively. The latter letter “G” specifies the tension

setting; 1 stands for no external tensioning and 2 stands for tensioned condition.

Winding angle is next, called by the letter “A” and followed by 1, 2, 3, 4 or 5, which

are the winding angles of 25o, 45o, 54o, 65o, 90o respectively, remembering all the

tubes of these winding angles are reinforced with a single layer of hoop winding as

the outermost layer. The one last number after the dash shows the position of the test

tube obtained by sectioning the manufactured tubes into three parts. For example, the

tube that is reinforced with glass fiber, manufactured with extra tensioning, wound at

an angle configuration of [±54°/90], and was at the middle position of the

manufactured tube obtained from filament winding machine, is designated as

E2G2A3-2.

40

3.5 Strain Measurements

In the present work, UFRA-5-350-23 rosette type electrical resistance strain gauges

are employed for recording the strain data. The main test materials for the strain

gauge are metals, ceramics and composites. Operating temperature range of the

gauge is -20 to +150°C and the strain limit is 3% (30000×10-6). Strains in axial and

hoop directions can be measured simultaneously by the mentioned system. Figure 3.9

shows the UFRA-5-350-23 strain gauges.

Figure 3.9 Schematic representation of UFRA-5-350-23 strain gauge

For the installation of strain gauges, grease, rust, etc. at the bonding surface are

removed. The bonding surface is lightly polished with an abrasive paper to obtain a

smoother surface. Having a perfectly smooth surface is vital in strain gauge

installations because the quality of the bonding of the strain gauge to the test surface

is directly related with the smoothness of the surface. The strain gauges are fixed on

the tubes by their special CN adhesive. The lead wires originated from the strain

gauges are soldered to the connecting terminals of the strain gauge data acquisition

system. The acquisition system collects and records the data coming from each three

measurement units.

3.6 Testing Procedure

The internal pressure tests are performed according to the standard ASTM D1599-

99, “Standard Test Method for Resistance to Short-Time Hydraulic Pressure of

41

Plastic Pipe, Tubing, and Fittings”. The method covers the determination of the

resistance of either thermoplastic or reinforced thermosetting resin pipe, tubing, or

fittings to hydraulic pressure in a short time period, and consists of loading the tube

to failure in a short time interval by means of a hydraulic pressure.

The internal pressure test experimentation was carried out in the following sequence:

- The tubes that are fabricated by wet filament winding method and cut into

desired length are fixed to the end closures by means of an adhesive. The

adhesive employed is CIBA – GEIGY Araldite AV 138–Hardener HV 998

epoxy adhesive. Once the adhesive is applied, the tube and the end closure

system are placed in the furnace at 80°C for one hour to allow the adhesive to

cure.

- The internal liner is placed in the tube.

- The strain gauge is fixed in the middle portion of the tube by using its CN

adhesive.

- It is filled completely with water.

- The tube is attached to the hydraulic pressure system assuring no air is

entrapped.

- The cables originated from the connecting terminals of the data acquisition

system are connected to the strain gauges by soldering.

- Pressure is applied and increased uniformly and continuously, until the tube

fails. Meanwhile, the pressure increase and changes in the strain are

monitored and recorded.

- Using the necessary formulations, the strain and pressure data are evaluated

to obtain the mechanical characteristics.

3.7 Testing Reporting

For the internal pressure test, the pressure is increased uniformly and continuously by

means of the hydraulic test unit. Meanwhile, the strain data is recorded as well.

42

When the test ends, the pressure drops to zero and recording of strain data is ended.

Tests are reported as mentioned in ASTM D 1599-99 standard. By the end of the test,

the pressure and strain gauge data are studied in order to obtain the desired

mechanical parameters.

3.7.1 Record of the Data

The tube dimensions are noted before the internal pressure test starts. Once the test

starts, the internal pressure system and the strain gauge system start to record the

pressure and strain data simultaneously, and they continue recording until the tube

fails and the loading rate is recorded as well. After the failure, the maximum pressure

recorded and the failure modes are also reported.

The internal pressure system records a single pressure value each second, until the

tube fails. These pressure values are recorded in bars. The computer program returns

the pressure data in the form of a text document. The pressure recording system is

given in Figure 3.10.

Figure 3.10 Pressure recording system.

43

The strain gauge data acquisition system records three data for each three

measurement units per second and it returns the strain data in the form of a text

document. For the evaluation of data, in order to have a consistency with the pressure

values, the corresponding data recorded per second is considered for all measurement

units. The strain gauge data acquisition system is given in Figure 3.11.

Figure 3.11 Strain gauge data acquisition system.

3.7.2 Calculations

Pressure test system records the pressure data in bars. The hoop stresses that are

formed in the tubes are calculated according to the ASTM D1599-99 standard [9], by

using Equation (3.2).

44

ttdPS

2)( +

= (3.2)

where

S = hoop stress, MPa

P = internal pressure, MPa

d = average inside diameter, mm

t = minimum wall thickness, mm

More commonly, Equation (3.3) is employed in the hoop stress calculations. But in

order to keep consistency with the ASTM 1599-99 standard, Equation (3.2) is used in

this work.

tPdS2

= (3.3)

where

S = hoop stress, MPa

P = internal pressure, MPa

d = average inside diameter, mm

t = minimum wall thickness, mm

After converting the pressure values that are recorded in bars into stress values,

stress-strain curves are plotted for each test by employing the converted stress data

and the strain data that are recorded from the strain gauges. Hoop elastic constants of

the curves are evaluated and these results will be given in the following chapter.

45

CHAPTER IV

EXPERIMENTAL RESULTS

This chapter presents the internal pressure test results and the hoop elastic constants

determined experimentally for the test tubes. The bursting pressure test results then

will be represented in terms of performance factor, to form a reliable basis for

discussion of data in the next chapters.

4.1. Internal Pressure Test Results

In this section, the internal pressure test results for all the test tubes are presented, in

two major groups regarding their reinforcement types. The burst pressure data with

the data of maximum strain, which is formed during loading, are given.

4.1.1 Carbon Fiber Reinforced Tubes

Twenty three internal pressure tests are applied on Carbon fiber reinforced epoxy

tubes. The test results data for the tubes are given in Table 4.1. For the tubes where

strain gauge is damaged and stopped collecting data, “maximum strain formed”

column is left empty. The tests are recorded to be successful if bursting is achieved.

For the tubes E1 G2 A2 – 2, E1 G1 A3 – 1, E1 G1 A3 – 2, and E1 G2 A3 – 2,

bursting could not be achieved, but instead, the adhesive that is used to fix the test

tube to the end closure units could not be able to withstand the load and failed,

resulting in a sudden decrease in internal pressure. The tests performed on these

tubes are recorded to be unsuccessful, as the desired failure mode is not obtained.

46

In all tests, the pressure values that are recorded in bars are converted into stress

values, and compared them with the data obtained from strain gauges. The stress –

strain data for the carbon reinforced tubes of [±25°]3 [90°]1 , [±45°]3 [90°]1, [±54°]3

[90°]1, [±65°]4 [90°]1 and [90°]7 winding angle configurations is given in Figures 4.1,

4.2, 4.3, 4.4 and 4.5, respectively.

47

Table 4.1 The test results for carbon fiber reinforced tubes

Test Tube Number

Maximum Strain Formed

(mm/mm)

Maximum Strain

Recorded (mm/mm)

Average Outer

Diameter (mm)

Average Loading

Rate (bars/sec)

Loading Time (sec)

Maximum Pressure

Recorded (bars) Test Result

E1 G1 A1 - 1 0.012000 0.012000 64.66 10.5 14 147 SUCCESSFUL

E1 G1 A1 - 2 0.010200 0.010200 64.63 6.3 18 114 SUCCESSFUL

E1 G1 A1 - 4 0.010300 0.010300 63.26 9.1 13 118 SUCCESSFUL

E1 G2 A1 - 1 0.010300 0.010300 63.72 6 16 96 SUCCESSFUL

E1 G2 A1 - 2 0.010900 0.010900 63.78 9.8 8 78 SUCCESSFUL

E1 G2 A1 - 3 0.011400 0.011400 63.37 7.6 21 159 SUCCESSFUL

E1 G1 A2 - 1 - 0.012400 63.39 12.3 34 418 SUCCESSFUL

E1 G1 A2 - 2 0.012900 0.012900 63.74 13.6 31 422 SUCCESSFUL

E1 G2 A2 - 1 - 0.012900 63.56 14.2 29 382 SUCCESSFUL

E1 G2 A2 - 2 - 0.012700 63.51 13.9 29 404-NO FAILURE UNSUCCESSFUL

E1 G1 A3 - 1 0.006980 0.006980 63.2 12.5 30 372-NO FAILURE UNSUCCESSFUL


E1 G1 A3 - 3 0.007910 0.007910 63.26 13.1 43 540 SUCCESSFUL

E1 G2 A3 - 1 0.000327 0.000327 63.25 13.1 38 498 SUCCESSFUL


E1 G1 A4 - 1 0.000669 0.000669 63.63 11.8 12 141 SUCCESSFUL

E1 G1 A4 - 2 0.000766 0.000766 63.63 10 14 140 SUCCESSFUL

E1 G2 A4 - 1 0.001230 0.001230 63.73 8.9 15 134 SUCCESSFUL

E1 G2 A4 - 2 0.000822 0.000822 63.83 8.1 17 137 SUCCESSFUL

E1 G1 A5 - 1 0.001260 0.001260 63.9 1.7 10 17 SUCCESSFUL

E1 G1 A5 - 2 0.000707 0.000707 63.78 2 11 22 SUCCESSFUL

E1 G2 A5 - 1 0.001290 0.001290 62.72 3.7 7 26 SUCCESSFUL

E1 G2 A5 - 2 0.000216 0.000216 62.94 2 11 22 SUCCESSFUL

48

0.00

E+0

0

5.00

E+0

1

1.00

E+0

2

1.50

E+0

2

2.00

E+0

2

2.50

E+0

2

3.00

E+0

2

0.00

E+0

02.

00E

-03

4.00

E-0

36.

00E

-03

8.00

E-0

31.

00E

-02

1.20

E-0

21.

40E

-02

Str

ain

(mm

/mm

)

Stress (MPa)

E1G

1A1-

1E

1G1A

1-2

E1G

1A1-

4E

1G2A

1-1

E1G

2A1-

2E

1G2A

1-3

Fi

gure

4.1

The

stre

ss –

stra

in d

ata

for t

he c

arbo

n re

info

rced

tube

s of [

±25°

] 3 [9

0°] 1

win

ding

ang

le c

onfig

urat

ion

49

0.00

E+0

0

1.00

E+0

2

2.00

E+0

2

3.00

E+0

2

4.00

E+0

2

5.00

E+0

2

6.00

E+0

2

7.00

E+0

2

8.00

E+0

2

0.00

E+0

02.

00E

-03

4.00

E-0

36.

00E

-03

8.00

E-0

31.

00E

-02

1.20

E-0

21.

40E

-02

Str

ain

(mm

/mm

)

Stress (MPa)

E1G

1A2-

1E

1G1A

2-2

E1G

2A2-

1E

1G2A

2-2

Fi

gure

4.2

The

stre

ss –

stra

in d

ata

for t

he c

arbo

n re

info

rced

tube

s of [

±45°

] 3 [9

0°] 1

win

ding

ang

le c

onfig

urat

ion

50

0,00

E+0

0

2,00

E+0

2

4,00

E+0

2

6,00

E+0

2

8,00

E+0

2

1,00

E+0

3

1,20

E+0

3

0,00

E+0

01,

00E

-03

2,00

E-0

33,

00E

-03

4,00

E-0

35,

00E

-03

6,00

E-0

37,

00E

-03

8,00

E-0

39,

00E

-03

Str

ain

(mm

/mm

)

Stress (MPa)

E1G

1A3-

1E

1G1A

3-2

E1G

1A3-

3E

1G2A

3-1

E1G

2A3-

2

Fi

gure

4.3

The

stre

ss –

stra

in d

ata

for t

he c

arbo

n re

info

rced

tube

s of [

±54°

] 3 [9

0°] 1

win

ding

ang

le c

onfig

urat

ion.

51

0.00

E+00

5.00

E+01

1.00

E+02

1.50

E+02

2.00

E+02

2.50

E+02

3.00

E+02 0.00

E+00

1.00

E-04

2.00

E-04

3.00

E-04

4.00

E-04

5.00

E-04

6.00

E-04

7.00

E-04

8.00

E-04

9.00

E-04

Stra

in (m

m/m

m)

Stress (MPa)

E1G

1A4-

1E1

G1A

4-2

E1G

2A4-

1E1

G2A

4-2

Fi

gure

4.4

The

stre

ss –

stra

in d

ata

for t

he c

arbo

n re

info

rced

tube

s of [

±65°

] 4 [9

0°] 1

win

ding

ang

le c

onfig

urat

ion.

52

0.00

E+00

1.00

E+01

2.00

E+01

3.00

E+01

4.00

E+01

5.00

E+01

6.00

E+01

7.00

E+01 0.00

E+0

05.

00E-

041.

00E-

031.

50E-

032.

00E-

032.

50E-

03

Stra

in (m

m/m

m)

Stress (MPa)

E1G

1A5-

1E1

G1A

5-2

E1G

2A5-

1E1

G2A

5-2

r t

he c

arbo

n re

info

rced

tube

s of

Figu

re 4

.5 T

he st

ress

– st

rain

dat

a fo

[90°

] 7 w

indi

ng a

ngle

con

figur

atio

n.

53

4.1.2 Glass Fiber Reinforced Tubes

Thirty internal pressure tests are applied on glass fiber reinforced epoxy tubes. The

test results data for the tubes are given in Table 4.2. For the tubes E2 G2 A2 – 1, E2

G2 A2 – 5, E2 G1 A3 – 1, E2 G1 A3 – 2 and E2 G1 A3 – 4, bursting could not be

achieved, but instead, the adhesive that is used to fix the test tube to the end closure

units could not be able to withstand the load and failed, resulting in a sudden

decrease in internal pressure. The tests performed on these tubes are recorded to be

unsuccessful, as the desired failure mode is not obtained. The pressure values for the

tubes E2 G2 A1 – 2, E2 G2 A1 – 4 and E2 G2 A2 – 2 could not be recorded due to a

problem in the internal pressure data recording system.

In all tests, the pressure values that are recorded in bars are converted into stress

values, and compared them with the data obtained from strain gauges. The stress –

strain data for the glass reinforced tubes of [±25°]2 [90°]1 , [±45°]2 [90°]1, [±54°]2

[90°]1, [±65°]3 [90°]1 and [90°]5 winding angle configurations is given in Figures 4.6,

4.7, 4.8, 4.9 and 4.10, respectively.

54

Table 4.2 Test results for glass fiber reinforced tubes

Test Tube Number

Maximum Strain Formed

(mm/mm)

Maximum Strain

Recorded (mm/mm)

Average Outer

Diameter (mm)

Average Loading

Rate (bars/sec)

Loading Time (sec)

Maximum Pressure

Recorded (bars) Test Result

E2 G1 A1 - 5 - 0.022400 63.78 8.7 27 236 SUCCESSFUL

E2 G1 A1 - 6 - 0.012600 64.62 7.3 30 220 SUCCESSFUL

E2 G2 A1 - 1 - 0.010500 64.34 6.1 15 91 SUCCESSFUL

E2 G2 A1 - 2 - 0.011900 64.11 - - NO PRESSURE DATA SUCCESSFUL


E2 G2 A1 - 5 - 0.012700 64.9 6.7 29 194 SUCCESSFUL

E2 G2 A1 - 6 - 0.010400 64.39 8.7 21 183 SUCCESSFUL

E2 G1 A2 - 1 - 0.012600 64.3 9.3 40 371 SUCCESSFUL

E2 G1 A2 - 2 - 0.012500 64.27 9.9 40 396 SUCCESSFUL

E2 G2 A2 - 1 - 0.012200 63.23 6.9 52 359-NO FAILURE UNSUCCESSFUL


E2 G2 A2 - 3 - 0.011700 64.29 10.5 26 274 SUCCESSFUL

E2 G2 A2 - 4 - 0.012400 64.28 8.9 32 285 SUCCESSFUL

E2 G2 A2 - 5 - 0.012200 64.29 7 23 160-NO FAILURE UNSUCCESSFUL



E2 G1 A3 - 4 - 0.012000 64.28 10 45 450-NO FAILURE UNSUCCESSFUL

E2 G1 A3 - 5 - 0.012100 64.57 10 43 425 SUCCESSFUL

E2 G2 A3 - 1 - 0.011900 64.14 10.9 24 471 SUCCESSFUL

E2 G2 A3 - 2 0.010900 0.010900 63.94 9.5 43 457 SUCCESSFUL

E2 G1 A4 - 4 0.011400 0.011400 65.17 5.4 21 114 SUCCESSFUL

55

0.00

E+00

5.00

E+01

1.00

E+02

1.50

E+02

2.00

E+02

2.50

E+02

3.00

E+02

3.50

E+02 0.

00E+

005.

00E-

031.

00E-

021.

50E-

022.

00E-

022.

50E-

02

Stra

in (m

m/m

m)

Stress (MPa)

E2G

1A1-

4E2

G1A

1-5

E2G

1A1-

6E2

G2A

1-1

E2G

2A1-

5E2

G2A

1-6

Fi

gure

4.6

The

stre

ss –

stra

in d

ata

for t

he g

lass

rein

forc

ed tu

bes o

f [±2

5°] 2

[90°

] 1 w

indi

ng a

ngle

con

figur

atio

n.

56

0.00

E+0

0

5.00

E+0

1

1.00

E+0

2

1.50

E+0

2

2.00

E+0

2

2.50

E+0

2

3.00

E+0

2

3.50

E+0

2

0.00

E+0

02.

00E

-03

4.00

E-0

36.

00E

-03

8.00

E-0

31.

00E

-02

1.20

E-0

21.

40E

-02

Str

ain

(mm

/mm

)

Stress (MPa)

E2G

1A2-

1E

2G1A

2-2

E2G

2A2-

1E

2G2A

2-3

E2G

2A2-

4E

2G2A

2-5

Fi

gure

4.7

The

stre

ss –

stra

in d

ata

for t

he g

lass

rein

forc

ed tu

bes o

f [±4

5°] 2

[90°

] 1 w

indi

ng a

ngle

con

figur

atio

n.

57

0.00

E+0

0

1.00

E+0

2

2.00

E+0

2

3.00

E+0

2

4.00

E+0

2

5.00

E+0

2

6.00

E+0

2

7.00

E+0

2

8.00

E+0

2

-2.0

0E-0

30.

00E

+00

2.00

E-0

34.

00E

-03

6.00

E-0

38.

00E

-03

1.00

E-0

21.

20E

-02

1.40

E-0

2

Stra

in (m

m/m

m)

Stress (MPa)

E2G

1A3-

1E

2G1A

3-2

E2G

1A3-

5E

2G2A

3-1

E2G

2A3-

2

Fi

gure

4.8

The

stre

ss –

stra

in d

ata

for t

he g

lass

rein

forc

ed tu

bes o

f [±5

4°] 2

[90°

] 1 w

indi

ng a

ngle

con

figur

atio

n.

58

0.00

E+00

2.00

E+01

4.00

E+01

6.00

E+01

8.00

E+01

1.00

E+02

1.20

E+02

1.40

E+02

1.60

E+02

-4.0

0E-0

3-2

.00E

-03

0.00

E+0

02.

00E-

034.

00E

-03

6.00

E-03

8.00

E-03

1.00

E-02

1.20

E-0

21.

40E-

02

Stra

in (m

m/m

m)

Stress (MPa)

E2G

1A4-

4E2

G1A

4-5

E2G

2A4-

4E2

G2A

4-5

Fi

gure

4.9

The

stre

ss –

stra

in d

ata

for t

he g

lass

rein

forc

ed tu

bes o

f [±6

5°] 3

[90°

] 1 w

indi

ng a

ngle

con

figur

atio

n.

59

0.00

E+0

0

5.00

E+0

0

1.00

E+0

1

1.50

E+0

1

2.00

E+0

1

2.50

E+0

1

3.00

E+0

1

3.50

E+0

1

4.00

E+0

1

4.50

E+0

1

-1.0

0E-0

40.

00E

+00

1.00

E-0

42.

00E

-04

3.00

E-0

44.

00E

-04

5.00

E-0

4

Str

ain

(mm

/mm

)

Stress (MPa)E

2G1A

5-1

E2G

1A5-

2E

2G2A

5-4

E2G

2A5-

5

Fi

gure

4.1

0 Th

e st

ress

– st

rain

dat

a fo

r the

gla

ss re

info

rced

tube

s of [

90°]

5 w

indi

ng a

ngle

con

figur

atio

n.

60

4.2. Performance Factors

As discussed in the previous chapters, tex values for the glass and carbon

reinforcements employed in this work are different with each other. This difference

brings a dissimilarity in the wall thicknesses of the tubes, although the number of

layers wound are similar. To fully wrap the surface of the mandrel, nearly same

length of fiber is used during the production of all tubes, but as the linear density of

the glass fibers is higher than that of carbon fiber, even the same number of layers of

winding result in different wall thicknesses, that is, wall thicknesses of glass

reinforced tubes are larger than the wall thicknesses of carbon reinforced tubes, for

the same winding angle configuration. Besides, the change in winding angle

configuration and extra tensioning may also lead to differences in wall thicknesses of

the tubes, even if the number of layers wound are the same or similar.

The burst pressure is used to calculate the stresses on the tube, but since the burst

pressure is strongly dependent on the wall thicknesses and the wall thicknesses are

different for each tube, it would be better to discuss the burst pressure data in terms

of the performance factor. The performance factor makes the burst pressure data

independent of the effect of the wall thickness.

Performance factor, N, is determined by Equation 4.1.

N = PV/W (4.1)

where

P: burst pressure, Pa

V: internal volume of the tube, m3

W: weight of the tube, kg

61

The performance factors of the test tubes are given in Table 4.3. The obtained values

for the performance factor are multiplied by a factor of 10-3, in order to have a better

visualization of the data.

Table 4.3 Burst performance factors for the test tubes.

Test Tube

Number

Test Result

(bars)

Test

Results

(Pa)

Weight

(kg)

Weight

(N)

Vin

(m3)

N

(1/m)

N*10-3

(1/m)

E1 G1 A1 - 1 147 14700000 0.316 3.0968 0.00113 5365.823 5.37 E1 G1 A1 - 2 114 11400000 0.316 3.0968 0.00113 4161.25 4.16 E1 G1 A1 - 4 118 11800000 0.316 3.0968 0.00113 4307.259 4.31 E1 G2 A1 - 1 96 9600000 0.316 3.0968 0.00113 3504.211 3.50 E1 G2 A1 - 2 78 7800000 0.316 3.0968 0.00113 2847.171 2.85 E1 G2 A1 - 3 159 15900000 0.316 3.0968 0.00113 5803.849 5.80 E1 G1 A2 - 1 418 41800000 0.324 3.1752 0.00113 14881.18 14.88 E1 G1 A2 - 2 422 42200000 0.324 3.1752 0.00113 15023.58 15.02 E1 G2 A2 - 1 382 38200000 0.313 3.0674 0.00113 14077.49 14.08

E1 G2 A2 - 2 NO

FAILURE - 0.313 3.0674 0.00113 - -

E1 G1 A3 - 1 NO

FAILURE - 0.308 3.0184 0.00113 - -

E1 G1 A3 - 2 NO

FAILURE - 0.308 3.0184 0.00113 - -

E1 G1 A3 - 3 540 54000000 0.308 3.0184 0.00113 20223.16 20.22 E1 G2 A3 - 1 498 49800000 0.308 3.0184 0.00113 18650.25 18.65

E1 G2 A3 - 2 NO

FAILURE - 0.308 3.0184 0.00113 - -

E1 G1 A4 - 1 141 14100000 0.332 3.2536 0.00113 4898.771 4.90

E1 G1 A4 - 2 140 14000000 0.332 3.2536 0.00113 4864.028 4.86

E1 G2 A4 - 1 134 13400000 0.332 3.2536 0.00113 4655.569 4.66

E1 G2 A4 - 2 137 13700000 0.332 3.2536 0.00113 4759.798 4.76

E1 G1 A5 - 1 17 1700000 0.28 2.744 0.00113 700.3207 0.70

E1 G1 A5 - 2 22 2200000 0.28 2.744 0.00113 906.2974 0.91

62


Test Tube

Number

Test Result

(bars)

Test Results

(Pa)

Weight

(kg)

Weight

(N)

Vin

(m3) N

(1/m)

N*10-3

(1/m)

E1 G2 A5 - 1 26 2600000 0.269 2.6362 0.00113 1114.877 1.11

E1 G2 A5 - 2 22 2200000 0.269 2.6362 0.00113 943.3579 0.94

E2 G1 A1 - 4 220 22000000 0.524 5.1352 0.00113 4842.81 4.84

E2 G1 A1 - 5 236 23600000 0.524 5.1352 0.00113 5195.015 5.20

E2 G1 A1 - 6 220 22000000 0.524 5.1352 0.00113 4842.81 4.84

E2 G2 A1 - 1 91 9100000 0.525 5.145 0.00113 1999.347 2.00

E2 G2 A1 - 2 NO P DATA - 0.525 5.145 0.00113 - -

E2 G2 A1 - 4 NO P DATA - 0.528 5.1744 0.00113 - -

E2 G2 A1 - 5 194 19400000 0.528 5.1744 0.00113 4238.126 4.24

E2 G2 A1 - 6 183 18300000 0.528 5.1744 0.00113 3997.82 4.00

E2 G1 A2 - 1 371 37100000 0.528 5.1744 0.00113 8104.87 8.10

E2 G1 A2 - 2 396 39600000 0.528 5.1744 0.00113 8651.02 8.65

E2 G2 A2 - 1 NO

FAILURE - 0.525 5.145 0.00113 - -

E2 G2 A2 - 2 NO P DATA - 0.525 5.145 0.00113 - -

E2 G2 A2 - 3 274 27400000 0.525 5.145 0.00113 6020.012 6.02

E2 G2 A2 - 4 285 28500000 0.525 5.145 0.00113 6261.691 6.26

E2 G2 A2 - 5 NO

FAILURE - 0.525 5.145 0.00113 - -

E2 G1 A3 - 1 NO

FAILURE - 0.506 4.9588 0.00113 - -

E2 G1 A3 - 2 NO

FAILURE - 0.506 4.9588 0.00113 - -

E2 G1 A3 - 4 450 45000000 0.506 4.9588 0.00113 10258.13 10.26

E2 G1 A3 - 5 425 42500000 0.506 4.9588 0.00113 9688.231 9.69

E2 G2 A3 - 1 471 47100000 0.508 4.9784 0.00113 10694.57 10.69

E2 G2 A3 - 2 457 45700000 0.508 4.9784 0.00113 10376.68 10.38

E2 G1 A4 - 4 114 11400000 0.556 5.4488 0.00113 2365.027 2.37

E2 G1 A4 - 5 120 12000000 0.556 5.4488 0.00113 2489.502 2.49

E2 G2 A4 - 4 110 11000000 0.555 5.439 0.00113 2286.156 2.29

E2 G2 A4 - 5 108 10800000 0.555 5.439 0.00113 2244.589 2.24

E2 G1 A5 - 1 17 1700000 0.476 4.6648 0.00113 411.9534 0.41

63


Test Tube

Number

Test Result

(bars)

Test Results

(Pa)

Weight

(kg)

Weight

(N)

Vin

(m3)

N

(1/m)

N*10-3

(1/m)

E2 G1 A5 - 2 10 1000000 0.476 4.6648 0.00113 242.3255 0.24

E2 G2 A5 - 4 17 1700000 0.483 4.7334 0.00113 405.983 0.41

E2 G2 A5 - 5 22 2200000 0.483 4.7334 0.00113 5.25E-08 0.53

4.3 Hoop Elastic Constants

During the evaluation of the stress – strain data, in order to minimize the errors that

can be originated from the strain gauges, special attention is paid on the strain gauge

data. The strain values that show inconsistency after a certain period of testing time

are disregarded with inconsistent data recorded at the beginning of some tests. At the

end of the tests, due to the very high strains formed in the tubes, which can even

exceed the measurement limit of the strain gauges, some illogical data are recorded.

These data are ignored as well.

Except the tubes of numbers E2G1A1 – 4, E2G1A1 – 5, E2G1A1 – 6, E2G2A1 – 5,

E2G2A1 – 6, E2G1A2-1, E2G1A2 – 2, E2G2A2 – 1, E2G2A2 – 3, E2G2A2 – 4,

E2G2A2 – 5, E2G1A3 – 1, E2G1A4 – 4, E2G1A4 – 5, all the stress – strain data

nearly lie linear and hoop elastic constants are determined without any trouble. For

the mentioned tubes, except E2G1A4 – 4, E2G1A4 – 5, the stress – strain curves

display regular changes in slope with increasing pressure values. For these tubes, the

first linear part of the curve is considered and evaluated to determine the hoop elastic

modulus. The reason for the difference in slopes and the resulting data will be

discussed in the following chapter. For the tubes of numbers E2G1A4 – 4, E2G1A4

– 5, the stress – strain data are rather unusual, and special attention will be paid for

their evaluation. The hoop elastic constants for the test tubes are given in Table 4.4.

64

Table 4.4. Hoop elastic constants for the tubes.

Test Tube Number Test Result (bars) E (GPa)

E1 G1 A1 - 1 147 20.9

E1 G1 A1 - 2 114 19.98

E1 G1 A1 - 4 118 17.35

E1 G2 A1 - 1 96 22.35

E1 G2 A1 - 2 78 18.93

E1 G2 A1 - 3 159 22.98

E1 G1 A2 - 1 418 49.54

E1 G1 A2 - 2 422 54.71

E1 G2 A2 - 1 382 47.84

E1 G2 A2 - 2 NO FAILURE 47.21



E1 G1 A3 - 3 540 115.7

E1 G2 A3 - 1 498 961.45


E1 G1 A4 - 1 141 166.36

E1 G1 A4 - 2 140 299.42

E1 G2 A4 - 1 134 199.873

E1 G2 A4 - 2 137 280.58

E1 G1 A5 - 1 17 29.89

E1 G1 A5 - 2 22 39.46

E1 G2 A5 - 1 26 284.16

E1 G2 A5 - 2 22 25.29

E2 G1 A1 - 4 220 37.82

E2 G1 A1 - 5 236 37.32

E2 G1 A1 - 6 220 27.94

E2 G2 A1 - 1 91 20.97

E2 G2 A1 - 2 NO P DATA -

65


Test Tube Number Test Result (bars) E (GPa)


E2 G2 A1 - 5 194 32.3

E2 G2 A1 - 6 183 17.82

E2 G1 A2 - 1 371 41.36

E2 G1 A2 - 2 396 37.46



E2 G2 A2 - 3 274 22.33

E2 G2 A2 - 4 285 40.26




E2 G1 A3 - 4 450

NO P DATA -

E2 G1 A3 - 5 425 53.12

E2 G2 A3 - 1 471 39.06

E2 G2 A3 - 2 457 52.31

E2 G1 A4 - 4 114 84.83

E2 G1 A4 - 5 120 78.24

E2 G2 A4 - 4 110 154.68

E2 G2 A4 - 5 108 92.72

E2 G1 A5 - 1 17 135.28

E2 G1 A5 - 2 10 69.76

E2 G2 A5 - 4 17 64.04

E2 G2 A5 - 5 22 88.83

66

As can be observed from the Table 5.1, hoop elastic constant values for the tubes E1

G2 A3 – 1, E1 G1 A4 – 2, E1 G2 A4 – 1, E1 G2 A4 – 2, E1 G2 A5 – 1, E2 G2 A4 –

4 and E2 G1 A5 – 1 are extremely high. Their irrationally high values are probably

due to some experimental errors originating from the strain gauge measurements.

Their evaluated hoop elastic modulus data will be ignored in discussions.

67

CHAPTER V

DISCUSSIONS

5.1. Burst Pressure Studies

In this section, the burst performance of the filament wound tubes are discussed, and

the effects of the process parameters (fiber type, extra tensioning for the fibers and

winding angle configuration) on the performance, is explained. As discussed in the

previous chapter, performance factors will be used in order to form a reliable basis

for comparison of data. Burst performance factor values are determined by taking the

average data from the tubes made of the same matrix and reinforcement, and of the

same winding angle configurations.

5.1.1 Effect of Winding Angle Configuration

Winding angle dependence of the burst pressure of the test tubes is discussed in

terms of burst performance factors. Figure 5.1 and 5.2 present the change in burst

performance factor of the carbon fiber reinforced tubes without and with extra

tensioning, respectively.

68

E1G1 SERIES

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80 90 100

winding angle [±o][90o]

N*1

0-3 (1

/m)

Figure 5.1. Burst performance factors for the carbon fiber reinforced tubes

manufactured without extra tensioning.

E1G2 SERIES

0

5

10

15

20

0 10 20 30 40 50 60 70 80 90 100


N*10

-3 (1

/m)

Figure 5.2. Burst performance factors for the carbon fiber reinforced tubes

manufactured with extra tensioning.

69

Figure 5.3 and 5.4 presents the change in burst performance factor of the glass fiber

reinforced tubes with and without tensioning, respectively.

E2G1 SERIES

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100

winding angle[±o][90o]

N*1

0-3 (1

/m)

Figure 5.3. Burst performance factors for the glass fiber reinforced tubes

manufactured without extra tensioning.

E2G2 SERIES

0

2

4

6

8

10

12

0 10 20 30 40 50 60 70 80 90 100


N*1

0-3 (1

/m)

Figure 5.4. Burst performance factors for the glass fiber reinforced tubes

manufactured with extra tensioning.

70

It can be observed from the Figures 5.1, 5.2, 5.3 and 5.4 that under internal pressure,

the burst pressure performance increases with increasing winding angle

configuration, reaches to maximum at the winding angle configuration of

[±54°][90°] for both fiber types and tensioning conditions, and for larger winding

configurations than [±54°][90°], the burst pressure performance decreases. The

variation in the burst performance with changing winding angle configuration is

expected, as the composite materials show an anisotropic behavior under different

loading conditions. Being highly anisotropic, when loaded in the direction of the

fiber alignment, composite materials are likely to exhibit the best mechanical

properties. For hoop loading condition, as the winding angle increases, the fiber

alignment direction becomes closer to the loading direction, and for [90°] winding

configuration, where the loading direction is the same as fiber alignment direction, it

shall show a maximum. On the other hand, as the winding angle increases, the

resistance of the composite tube to axial load decreases. The hoop layer present as

the outermost layer of all the tubes increases the hoop strength significantly, but it

has a very low resistance to axial loads. Internal pressure loading is a combined

loading type, it creates both axial and hoop stresses in the material, and thus the

maximum performance is expected to be attained in the winding configuration which

optimizes the resistances to hoop and axial stresses. The increase in the burst

performance of the test tubes with increasing winding angle configuration is thus

expected, and can be explained by higher hoop resistances being dominant over

lower axial resistances as the winding angle configuration increases. After the

maximum, the detected decrease can be said to be due to the dominant lowering in

axial mechanical resistance over increasing hoop resistance. Considering this,

[±54°][90°] being the best winding configuration is an expected result, as it can be

verified from the several data in literature [27, 28].

5.1.2 Effect of Extra Fiber Tensioning

Tension setting dependence of the burst pressure of the test tubes is also discussed in

terms of burst performance factors. The effect of extra tensioning on burst

71

performance factors of the carbon fiber reinforced and glass fiber reinforced tubes

can be observed from Figure 5.5 and 5.6, respectively.

E1 SERIES

0

5

10

15

20

25

0 20 40 60 80 100


N*1

0-3 (1

/m)

without extra tensioningwith extra tensioning

Figure 5.5. Burst performance factors for the carbon fiber reinforced tubes.

E2 SERIES

0

2

4

6

8

10

12

0 20 40 60 80 100


N*1

0-3 (1

/m)


Figure 5.6 Burst performance factors for the glass fiber reinforced tubes.

72

Examining the figures, it can be seen that for carbon fiber reinforced tubes, the effect

of extra tensioning is not significant, that is, the performance factor values for both

tension settings lie in the same range for every winding angle. For glass fiber

reinforced tubes, although extra tensioning seems to decrease the performance

factors for the winding angles lower than [±54°][90°], it can be said that the decrease

in the [±45°][90°] winding configuration burst pressure is probably due to another

reason discussed in the previous chapter. The lower burst pressure data of those tubes

that are subjected to excessive grinding of the tube surface for the fixing of the strain

gauges resulted in the loss of a part of the outermost layer of the tubes. During the

tests, it was observed that the failure started at these regions where an excessive

grinding was present and the burst pressures are quite lower than expected. An

evidence for that is that a similar tube that belongs to the same parent tube withstood

an internal pressure of 359 bar without failure, whose performance factor could not

be evaluated because a successful catastrophic failure could not be obtained. For the

winding angles above [±54°][90°], the effect of extra tensioning is not significant,

and extra tensioning need not necessarily be considered while optimizing the process

parameters for maximum burst performance.

5.1.3 Effect of the Type of Reinforcement Material

Fiber type is another production parameter considered in this work. The burst

performance of the two types of the fibers used can be seen in Figures 5.7 and 5.8 for

the tubes manufactures without extra tensioning and with extra tensioning,

respectively.

73

G1 SERIES

0

5

10

15

20

25

0 20 40 60 80 100


N*1

0-3 (1

/m)

carbon fiber reinforcedglass fiber reinforced

Figure 5.7 Burst performance factors of the tubes without extra tensioning.

G2 SERIES

0

5

10

15

20

0 20 40 60 80 100


N*1

0-3 (1

/m)

carbon fiber reinforced glass fiber reinforced

Figure 5.8 Burst performance factors of the tubes with extra tensioning.

74

Examining the figures, it can be seen that carbon fiber reinforced tubes show a much

better burst performance compared to the glass fiber reinforced ones. This is an

expected result considering that carbon fibers are much stronger and stiffer than the

glass fibers.

An overall look at the burst pressure performance factors is given in Figure 5.9.

BURST PRESSURE PERFORMANCE FACTOR

0

5

10

15

20

25

0 20 40 60 80 100


N*1

0-3 (1

/m) E1G1 series

E1G2 seriesE2G1 seriesE2G2 series

Figure 5.9 Burst pressure performance factors.

As a result, considering the test results, when the burst pressure performance is of

primary importance for the filament wound tubes, it can be said that carbon fiber

reinforced tubes with the winding configuration of [±54°][90°], shall be the best

choice for such internal pressure applications. Extra tensioning is observed not to

have a significant effect on burst pressure performance.

75

5.2 Hoop Elastic Constant Studies

This section will discuss the hoop elastic constants of the filament wound tubes,

obtained by evaluating the hoop stress – strain data presented in the previous chapter.

The effects of winding angle configuration, extra tensioning for fibers and the fiber

type will also be discussed.

5.2.1 Effect of Winding Angle Configuration

In Figure 5.10 and 5.11, the changes in the hoop elastic constants of the carbon fiber

reinforced tubes, manufactured with different winding angles are compared for the

tubes manufactured without and with extra tensioning, respectively.

E1G1 SERIES

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100


E (G

Pa)

Figure 5.10 Hoop elastic constant of the carbon fiber reinforced tubes manufactured

without extra tensioning.

76

E1G2 SERIES

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100


E (G

Pa)

Figure 5.11 Hoop elastic constant of the carbon fiber reinforced tubes manufactured

with extra tensioning.

Figures 5.12 and 5.13 present the change in hoop elastic constants of the glass fiber

reinforced tubes with and without tensioning, respectively.

E2G1 SERIES

0102030405060708090

0 10 20 30 40 50 60 70 80 90 100


E (G

Pa)

Figure 5.12 Hoop elastic constant of the glass fiber reinforced tubes manufactured

without extra tensioning.

77

E2G2 SERIES

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70 80 90 100


E (G

Pa)

Figure 5.13 Hoop elastic constant of the glass fiber reinforced tubes manufactured

with extra tensioning.

It is seen from the figures that for both fiber types and extra tensioning conditions,

the hoop elastic constants increase with the increasing winding angle configuration,

reaching to maximum at the winding angle configuration of [±65°][90°], and

decreases for greater winding configurations, [90°]. Like the burst pressure

performance, this behavior can be related to the anisotropic behavior of the

composites. The elastic constants and stiffness values for the composites when

loaded in their fiber alignment condition, exhibit a maximum and as the winding

angle decreases, the elastic constant in the hoop loading direction also decreases. For

the configuration of [±65°][90°], the resistance to loading in hoop direction is so

large that the tube expands in axial direction much more than it does in hoop

direction. As a result of this, the strain gauges give lower deformations and thus

higher hoop elastic constant compared to the tensile elastic constant in fiber

direction, E11. For the configuration of [90°], the expansion in hoop direction is very

hard and limited, and the tube would like to expand in axial direction instead. But,

due to the very low pressure resistance of the configuration in axial direction, it

cannot elongate in axial direction and so it cannot decrease the expansion in hoop

78

direction as it fails very quickly due to the axial loads. As a result, the elastic

constant of [90°] winding angle configuration is lower than expected.

5.2.2 Effect of Extra Fiber Tensioning

The effect of extra tensioning on burst performance factors of the carbon fiber

reinforced and glass fiber reinforced tubes can be observed from Figure 5.14 and

5.15, respectively.

E1 SERIES

0

50

100

150

200

250

0 20 40 60 80 100


E (G

Pa) without extra tensioning

with extra tensioning

Figure 5.14 Hoop elastic constants of the carbon fiber reinforced tubes.

79

E2 SERIES

0

20

40

60

80

100

120

0 20 40 60 80 100


E (G

Pa)


Figure 5.15 Hoop elastic constants of the glass fiber reinforced tubes.

Examining the figures, it can be seen that for carbon fiber reinforced tubes, the effect

of extra tensioning is not significant on the hoop elastic constant values, that is, the

hoop elastic constant values for both tension settings lie in the same range for every

winding angle. On the other hand, for glass fiber reinforced tubes, extra tensioning

seems to increase the hoop elastic constant considerably for the [±65°][90°] winding

configuration. This unexpected increase is probably due to unusual stress – strain

data exhibited by glass fiber reinforced tubes produced by this winding

configuration, which is given in the previous chapter. The strain response of the tube

to internal pressure load is very limited in the first part of loading, and it exhibits

very low strains that results in hoop elastic constants even higher than that of single

glass fiber. During the test, it was observed that the failure mode of the [±65°][90°]

tubes are quite different than expected as well, which, will be discussed in the

following section. The first part of the stress – strain curve has a very high slope as

mentioned, and once the failure begins, the strain response changes and the strains

formed in the tube increase with the increasing load, which results in a lower slope

and thus hoop elastic constant. This failure can be observed during the test as

formation of subsections at the tube that move free from each other, which will also

80

be discussed in the following section. Other than that, considering the figures, it can

be said that the effect of extra tensioning is not significant, and extra tensioning need

not necessarily be considered while optimizing the process parameters for maximum

burst performance. It follows that extra tensioning does not in any case increase the

fiber wetting and so does not affect the bonding.

5.2.3 Effect of the Type of Reinforcement Material

The hoop elastic constants of the two types of the fibers used are presented in Figures

5.16 and 5.17 for the tubes manufactured without extra tensioning and with extra

tensioning, respectively.

G1 SERIES

0

50

100

150

200

250

0 20 40 60 80 100


E (G

Pa)


Figure 5.16 Hoop elastic constants of the tubes without extra tensioning.

81

G2 SERIES

0

50

100

150

200

250

0 20 40 60 80 100


E (G

Pa)


Figure 5.17 Hoop elastic constants of the tubes with extra tensioning.

Examining the figures, it can be seen that carbon fiber reinforced tubes exhibit a

much larger hoop elastic constants compared to the glass fiber reinforced ones. The

increase in the hoop elastic constant with increasing angle before reaching to a

maximum becomes much significant for the carbon reinforced tubes. This is an

expected result considering that carbon fibers are much more anisotropic; are

stronger and stiffer than the glass fibers in the hoop loading direction but the

degradation of the mechanical properties of the carbon fiber reinforced structures

becomes more pronounceable for the lower winding angles.

An overall look at the hoop elastic constants is given in Figure 5.18.

82

HOOP ELASTIC CONSTANTS

0

50

100

150

200

250

0 20 40 60 80 100


E (G

Pa) E1G1series

E1G2 seriesE2G1 seriesE2G2 series

Figure 5.18 Hoop elastic constants.

Considering the test results, when the high hoop elastic constant is of primary

importance for the filament wound tubes, it can be said that carbon fiber reinforced

tubes with the winding configuration of [±65°][90°], shall be the best choice for such

internal pressure applications. Extra tensioning is again observed not to have a

significant effect on burst pressure performance.

5.3 Failure Modes

As discussed in the previous chapters, the failure in the tests are required to be

catastrophic, that is, bursting is desired. In order to assure catastrophic failure,

elastomeric internal liners are placed in the test tubes, which are to prevent any

leakage from the possible matrix cracks and accordingly avoid a decrease in the

internal pressure before catastrophic failure occurs.

During the experiments, the failure modes that can be seen are ply failures that take

place in the outermost layer and simple catastrophic failures, where all the layers fail

at the same time. Any ply failure that originates in the inner layers, but not the

83

outermost layer cannot be observed during experiment, but can be figured out from

the evaluation of the stress – strain data.

For the winding configuration of [±25°]3 [90°]1, carbon reinforced tubes except

E1G2A1-1, exhibit a regular stress – strain data, that is, no considerable change is

slope is observed and the curve is almost linear until failure. This implies that the

failure that occurred may simply be catastrophic, that is, all the layers have failed at

the same time. Another possibility is that first ply failure has taken place first, and

the time interval between the first ply failure and final failure is so short that the

recording speed of the strain gauge data acquisition system was unable to detect that

possible ply failure, and indicate it in the stress – strain curve. An example of a failed

carbon fiber reinforced tube of [±25°]3 [90°]1 winding configuration is given in

Figure 5.19. For the glass fiber reinforced tubes of [±25°]2 [90°]1 winding

configuration, significant changes in the slopes of the stress – strain curves are

observed. These changes form multiple elastic constant values in the tube at different

loading times. The reason for that change is probably ply failures of inner layers. In a

laminate, each ply tends to perform as though itself and when one of the plies in the

structure starts to fail, it cracks the matrix around and there appears an increase in the

strain and thus the slope decreases. When the first ply failure is completed, the

structure starts to behave in its original way, as one ply is completely gone and other

plies stand intact. The strain response of the tube is restored but the load carrying

thickness of the tube is decreased due to the failure of one of the layers. As the wall

thickness of the tube is decreased, it cannot carry more load anymore, and fails. The

second and third slope values are the hoop elastic constant values for damaged tubes

and are not considered in this work. The reason is that this work aims to produce data

for the design applications and the structures are generally designed without failure

condition. An example of the failed glass fiber reinforced tube of [±25°]2 [90°]1

winding configuration is given in Figure 5.20.

84

Figure 5.19. Failed carbon fiber reinforced tube of [±25°]3 [90°]1 winding

configuration.

Figure 5.20. Failed glass fiber reinforced tube of [±25°]2 [90°]1 winding

configuration.

For the winding configuration of [±45°]3 [90°]1, carbon reinforced tubes exhibit a

regular stress – strain data, but some slight change in slopes are observed just before

failure. These changes are due to the first ply failures in the structure, and after the

first ply failure, the structure could not carry more load and failed catastrophically.

85

An example of a failed carbon fiber reinforced tube of [±45°]3 [90°]1 winding

configuration is given in Figure 5.21. For the glass fiber reinforced tubes of the

[±45°]2 [90°]1 winding configuration, significant changes in the slopes of the stress –

strain curves are observed. The reason for that change is probably the first ply

failures, and for the tube number E2G2A2-3, the stress – strain data implies multiple

changes in slope, that is, several ply failures. An example of the failed glass fiber

reinforced tube of [±45°]2 [90°]1 winding configuration is given in Figure 5.22.


configuration.

86


configuration.

For the winding configuration of [±54°]3 [90°]1, carbon reinforced tubes exhibit some

slight changes in slopes before failure. These changes are again due to the first ply

failures in the structure, and after the first ply failure, the structure could not carry the

high load and failed catastrophically. For the glass fiber reinforced tubes of the

[±54°]2 [90°]1 winding configuration, significant multiple changes in the slopes of

the stress – strain curves are observed, that is, several ply failures have taken place.

An example of the failed glass fiber reinforced tube of [±54°]2 [90°]1 winding

configuration is given in Figure 5.23.

87


configuration.

For the winding configuration of [±65°]3 [90°]1, carbon reinforced tubes exhibit

slight changes in slopes before failure, which implies that first ply failure takes place

in the structure before the final failure. The final failure is catastrophic, and an

example of a failed carbon fiber reinforced tube of [±65°]3 [90°]1 winding

configuration is given in Figure 5.24. For the glass reinforced tubes of the same

winding configuration, during the internal pressure tests, a different type of failure is

observed. The tubes display an unusual, non-linear stress – strain curve. At the end of

the test, tube loses its integrity and subsections are formed, which, makes the outer

lining of the tube attain a wavy-like external appearance, but the internal pressure is

still not decreased and the tube has not failed yet although buckling has occurred and

subsections are formed. The reason for that appearance may be the failure of an

interior layer or layers, and thus falling apart of the structure, but remembering that

there lies an elastomeric liner inside, which holds the structure together, some

subsections are formed in the tube. Those subsections then start to behave almost

free from each other and wavy-like external appearance is observed. In other words,

winding configuration is comparably weak in axial direction and the tube cannot

carry more load, and the structure failed from the weak points and the tube started to

behave as if it was formed of free cylinders. After the formation of subsections, the

88

strain response of the structure changed as given in Figure 4.9. Thus, the sudden

decrease in the strains can probably be explained by the failure of one of the interior

layers and formation of subsections. These subsections can move in a less restricted

manner and this decreases the strain formed in the material. This failure mode can be

observed from the Figure 5.25.


configuration


configuration.

89

When the stress – strain data of the winding configuration of [90°] for carbon fiber

reinforced tubes are explored, the first point that calls attention is very low failure

pressures. The tubes simply fail in axial direction. The reason is that while the tubes

are extremely strong and stiff in their hoop direction, when internal loading starts, the

load finds a great resistance in hoop direction. Instead, strains in axial weak

directions become dominant. The structure cannot withstand more axial load and

fails in a short time interval, at low internal pressures. An example of a failed glass

reinforced tube of [90°]7 winding angle configuration is given in Figures 5.26

Figure 5.26. Failed glass fiber reinforced tube of [90°]5 winding configuration.

5.4 Comparison of the Burst Pressure Data with Laminate Analysis

A typical filament wound laminate consists of several plies oriented at arbitrary

angles and stacking sequence. In a laminate, each ply tends to perform as though by

itself, but behavior of each ply is modified to interact with the remaining plies of the

laminate. This interaction between the plies is important in composite laminate

performance and it affects the mechanical behavior. Laminate analysis is an

important tool in predicting the mechanical performance of the composite laminates.

90

In this study, “ASME Boiler and Pressure Vessel Code, Section X: Fiber-Reinforced

Plastic Pressure Vessels” is employed for the laminate analysis for the composite

tubes. Winding angle configuration, fiber and resin properties, number of layers and

wall thicknesses are the inputs, and the code evaluates and returns the burst pressure

and the first layer where the failure initiates. The results of the analysis are presented

with the experimental results in Table 5.1.

Table 5.1 Internal pressure test and ASME Boiler and Pressure Vessel Code, Section

X analysis results.

Test Tube

Number

Internal Pressure Test

Results (bars)

ASME Section X

Results (bars)

ASME Section X

Failure Layer

E1 G1 A1 - 1 147

E1 G1 A1 - 2 114

E1 G1 A1 - 4 118

90 inner layer

E1 G2 A1 - 1 96

E1 G2 A1 - 2 78

E1 G2 A1 - 3 159

80 inner layer

E1 G1 A2 - 1 418

E1 G1 A2 - 2 422 390 inner layer

E1 G2 A2 - 1 382

E1 G2 A2 - 2 NO FAILURE 385 inner layer

E1 G1 A3 - 1 NO FAILURE


E1 G1 A3 - 3 540

390 outermost layer

E1 G2 A3 - 1 498

E1 G2 A3 - 2 NO FAILURE 390 inner layer

E1 G1 A4 - 1 141

E1 G1 A4 - 2 140 135-155 outermost layer

E1 G2 A4 - 1 134

E1 G2 A4 - 2 137 135 - 155 outermost layer

91


Test Tube

Number


Results (bars)

ASME Section X

Results (bars)

ASME Section X

Failure Layer

E1 G1 A5 - 1 17

E1 G1 A5 - 2 22 55-60 all layers

E1 G2 A5 - 1 26

E1 G2 A5 - 2 22 55-60 all layers

E2 G1 A1 - 4 220

E2 G1 A1 - 5 236

E2 G1 A1 - 6 220

225 inner layer

E2 G2 A1 - 1 91

E2 G2 A1 - 2 NO PRESSURE DATA

E2 G2 A1 - 4 NO P

E2 G2 A1 - 5 194

E2 G2 A1 - 6 183

225 inner layer

E2 G1 A2 - 1 371



E2 G2 A2 - 2 NO PRESSURE DATA

E2 G2 A2 - 3 274

E2 G2 A2 - 4 285


370 inner layer



E2 G1 A3 - 4 450

E2 G1 A3 - 5 425

450 inner layer

E2 G2 A3 - 1 471


E2 G1 A4 - 4 114


E2 G2 A4 - 4 110


92


Test Tube

Number


Results (bars)

ASME Section X

Results (bars)

ASME Section X

Failure Layer

E2 G1 A5 - 1 17

E2 G1 A5 - 2 10 50-55 all layers

E2 G2 A5 - 4 17

E2 G2 A5 - 5 22 40-45 all layers

The results obtained from ASME Boiler and Pressure Vessel Code, Section X are

rather consistent with the experimental burst pressure test results, except being

slightly lower. This is an expected result remembering that there lies an elastomeric

internal liner inside the tubes. The liner also carries load during the experiments, but

it is not shown in laminate analysis. Exploring the results, it was observed that for

carbon fiber reinforced tubes manufactured with [±54°]3 [90°]1 winding angle

configuration, the laminate analysis give lower burst pressure data compared with the

experimental results. The reason is that, the laminate analysis mentions that the

failure starts from the outermost layer. According to the analysis, when a ply fails,

the structure is accepted to be failed and the code gives the first ply failure pressure

as the tube’s failure pressure. However, in reality, the structure is still capable of

carrying load, as observed in the experiment. During the experiment, the failure of

the outermost layer can be followed from the stress – strain data of the tube as a

change in slope, but the failure stress is much higher. Therefore, the higher burst

pressure value observed at the experiment is reasonable. For both fiber types, the

analysis results for [90°] winding angle configuration are higher than those of the

experimental results, which probably is due to the extremely low strength of the

winding configuration in axial direction, as discussed in the previous chapters.

Failure modes for the glass fiber reinforced tubes are consistent with the failure

modes deduced from their stress – strain data. Except the tubes of [90°] winding

angle configuration, ASME Boiler and Pressure Vessel Code claims all the failures

93

to originate at the inner layers, which is the case in the tests, and can be verified by

the changes in the slopes of the experimental stress – strain curves. The catastrophic

failure cannot be differentiated from the failures that originate at the inner layers and

for the carbon fiber reinforced tubes, it was concluded that experiments reveal no

significant difference for the failure mode, as the stress – strain data are linear until

failure. This suggested that all the layers might have failed instantly, that is, the

failure is catastrophic, which would conflict the analysis results. But as mentioned

before, another possibility is that the time interval between a possible first ply failure

and final failure is so short that the recording speed of the strain gauge data

acquisition system was unable to detect that first ply failure. As a result, it can be

said that the burst pressure data is consistent with the laminate analysis.

94

CHAPTER VI

CONCLUSION AND RECOMMENDATIONS The aim of the study was to to determine the mechanical characteristics of the

filament wound composite tubes working under internal pressure loads, by

experimentally measuring the mechanical properties like strains in hoop direction,

maximum hoop stresses that are formed during internal pressure loading. Doing that,

it was intended to identify and generate the necessary data to be used in the design

applications and path a way to a new research on life assessment with health

monitoring.

In order to determine the composite behavior, a total number of 52 internal pressure

tests are applied on the composite tubes that are manufactured with wet filament

winding method. The test are carried out according to ASTM D 1599-99 standard.

Two different fiber types (glass and carbon fibers), two different fiber tension

settings (default fiber tensioning and extra fiber tensioning) and five different

winding angles (25°, 45°, 54°, 65° and 90°, with a single layer of hoop reinforcement

on each) are employed in manufacturing of the tubes. The changes in internal

pressure and the burst pressure are recorded. The strain data of each tube are

obtained by strain gauges, and are evaluated with the stress data. Accordingly, the

mechanical properties of the tubes are summarized in Table 6.1 and Table 6.2 for

carbon and glass fiber reinforced tubes, respectively.

95

Table 6.1 Mechanical properties of carbon fiber reinforced tubes.

Winding Angle

Configuration [±°][90°]

Burst Pressure

(bars)

Hoop Elastic Constant

(GPa)

25 78 - 159 17.4 - 22.3

45 418 - 422 47.2 - 54.7

54 498 - 540 98.3 - 120.3

65 134-141 166.3 - 299.4

90 17 - 26 25.3 - 39.5

Table 6.2 Mechanical properties of glass fiber reinforced tubes.

Winding Angle

Configuration [±°][90°]

Burst Pressure

(bars)

Hoop Elastic Constant

(GPa)

25 91 - 236 17.8 - 37.8

45 274 -285 19.8 - 41.4

54 425 - 471 39 - 86

65 108 - 120 78.2 - 154.7

90 10 - 22 64 - 135.3

Evaluating the data, it was observed that carbon fiber reinforced tubes of

[±54°]3[90°]1 winding configuration shows the maximum burst performance. In

general evaluation, the carbon fiber reinforced tubes exhibited better performance

than glass fiber reinforced tubes. Also, [±54°][90°]1 winding configuration is the best

performance for both fiber types. It was observed that burst pressure and hoop elastic

constants are extensively dependent on the fiber type and winding angle

configuration, but the effect of extra tensioning of fibers is insignificant on burst

performance.

96

The burst pressure results are verified with the laminate analysis. “ASME Boiler and

Pressure Vessel Code, Section X: Fiber-Reinforced Plastic Pressure Vessels” is

employed in the laminate analysis. It was found that the burst pressure values and the

failure modes offered by the analysis are rather consistent with the experimental

results. The only significant difference in the results are for [90°] winding angle

configuration, and the reason is decided to be the extreme weakness of the

configuration in axial direction, which, resulted in the failure of the tube at very low

pressure values. It was observed that internal pressure testing is a reliable method in

determining the burst properties of filament wound structures.

In literature, internal pressure testing is commonly employed for the determination of

mechanical properties. The factor that differentiates this study from the similar ones

is that the tests in literature are applied to the composite tubes of lower wall

thicknesses, whereas rather larger wall thicknesses are employed in this work.

Filament winding operation significantly alters the microstructure and physical

properties for low thicknesses. Very low wall thicknesses may result in the failure of

the structure at the matrix regions, and thus, for successful simulation of the tests,

wall thicknesses must be above a certain value. Another point is that, this work is

almost able to simulate a pressure vessel, as there is a liner inside the structure, wall

thicknesses are fairly large, and free – end condition is accomplished at the tests.

Studying with the composites, it should always be remembered that the properties of

composites are not homogeneous throughout the structure. Their performance is

highly dependent on the fabrication processes and parameters, and they are very

sensitive to environmental conditions, storage and handling. Any defect or flaw that

is possibly introduced during these stages can easily degrade the mechanical

properties of the composites. This fact is once more verified by this work, as it was

observed that the tubes that even belonged to the same parent tube can reveal very

different performances. Due to this fact, it should again be emphasized that the

composite materials shall require very large safety factors in design applications.

97

The evaluation of the strains and the determination of the strain value where the first

failure is observed is very important for life assessment. For example, fatigue tests

are generally carried out at some predefined stress values, which are the fractions of

the strength of the material. The strain response of the composite to a certain value of

stress obviously influences its fatigue life. If the formed strain in a material is large

for constant stress, structure will deform easily and quicker, and thus the fatigue life

will be shorter. Therefore, for the design applications that consider fatigue life, it is

vital to know the strain response of the composite.

Another important aspect of the prediction of strain response of the composite may

be that, the critical applications in which the geometric tolerances are very low,

require low strains. High expansions and deformations are not permitted in those

practices. Excessive expansions of such parts in a system may result in the

degradation of the system properties of the overall structure. For design applications

that require low geometric tolerances, having a knowledge about the strain response

of the material is essential and crucial.

Considering the fatigue properties, a future study may be suggested as the

determination of the fatigue life of filament wound composite tubes. Internal

pressure fatigue life tests are carried out at certain predefined stress values, which are

the fractions of the burst pressure of the material. Studying the burst pressures of the

filament wound composite tubes that are manufactured with different production

parameters in this work, a further step may be suggested as fatigue life determination

of such structures by internal pressure testing.

The study considered the effects of the fiber type, winding angle configuration and

extra tensioning of fibers on mechanical properties, but, it should be recalled that

these variables are not the only production parameters of the filament winding

process which affect the performance of the filament wound structures. Resin bath

temperature, tex value of fibers, types of resin, winding patterns, winding ply

configurations, hybridization, curing conditions and surface treatment may also

98

influence the properties of filament wound structures. For filament winding process

optimization, a study that investigates the effect of these variables on mechanical

properties can be suggested as another future work.

99

REFERENCES

[1] S.K. Mazumdar, Composites Manufacturing: Materials, Product, and

Process Engineering, CRC Press, 2002.

[2] T. E. Miller, Introduction to Composites, Composites Institute Publications,

1990.

[3] J.W. Weeton, D.M. Peters, K.L. Thomas, Engineers’ Guide to Composite

Materials, ASM Publications, 1990.

[4] ASTM D 3878-98 Standard Terminology for Composite Materials, ASTM

Standard, 1998.

[5] N. L. Hancox, R. M. Mayer, Design Data For Reinforced Plastics, Chapman

& Hall, 1994.

[6] Carbon and High Performance Fibers, Directory and Databook, Edition 6,

Chapman & Hall, 1995.

[7] M. M. Schwartz, Composite Materials, Volume II: Processing, Fabrication,

and Applications, Prentice Hall Publications, 1997.

[8] ASTM D 2290-04 Standard Test Method for Apparent Hoop Tensile Strength

of Plastic or Reinforced Plastic Pipe by Split Disk Method, ASTM Standard,

2004.

100

[9] ASTM D 1599-99 Standard Test Method for Resistance to Short-Time

Hydraulic Pressure of Plastic Pipe, Tubing, and Fittings, ASTM Standard,

1999.

[10] ASTM D 2143-00 Standard Test Method for Cyclic Pressure Strength of

Reinforced, Thermosetting Plastic Pipe, ASTM Standard, 2000.

[11] ASTM D 2992-01 Standard Practice for Obtaining Hydrostatic or Pressure

Design Basis for Fiberglass (Glass-Fiber-Reinforced Thermosetting-Resin)

Pipe and Fittings, ASTM Standard, 2001.

[12] ASTM D 2105-01 Standard Test Method for Longitudinal Tensile Properties

of Fiberglass (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe and Tube,

ASTM Standard, 2001.

[13] ASTM F 948-94(2001)e1 Standard Test Method for Time-to-Failure of

Plastic Piping Systems and Components Under Constant Internal Pressure

With Flow, ASTM Standard, 2001.

[14] ASTM D 3410/D3410M-03 Standard Test Method for Compressive

Properties of Polymer Matrix Composite Materials with Unsupported Gage

Section by Shear Loading, ASTM Standard, 2003.

[15] ASTM D 3479/D3479M-96(2002)e1 Standard Test Method for Tension-

Tension Fatigue of Polymer Matrix Composite Materials, ASTM Standard,

2002.

101

[16] ASTM D 3518/D3518M-94(2001) Standard Test Method for In-Plane Shear

Response of Polymer Matrix Composite Materials by Tensile Test of a ± 45o

Laminate, ASTM Standard, 2001.

[17] P. Mertiny, F. Ellyin, and A. Hothan, An Experimental Investigation on the

Effect of Multi-Angle Filament Winding on the Strength of Tubular

Composite Structures, Composites Science and Technology, Vol 64, pp. 1-9,

2004

[18] P.D. Soden, R. Kitching, P.C. Tse, Y. Tsavalas, Influence of Winding Angle

on the Strength and Deformation of Filament Wound Composite Tubes

Subjected to Uniaxial and Biaxial Loads, Composites Science and

Technology, Vol 46, pp. 363-378, 1992.

[19] P.D. Soden, R. Kitching, P.C. Tse, Experimental Failure Stresses for ±55°

Filament Wound Glass Fiber Reinforced Plastic Tubes Under Biaxial Loads,

Composites, Vol 20, Number 2, pp 125-134, 1989

[20] F. Ellyin, M. Carroll, D. Kujawski and A.S. Chiu, The Behavior of

Multidirectional Filament Wound Fibreglass/Epoxy Tubulars Under Biaxial

Loading, Composites Part A: Applied Science and Manufacturing, Vol 28, pp

781-790, 1997

[21] N.Tarakçioğlu, L.Gemi and A.Yapıcı, Fatigue Failure Behavior of

Glass/Epoxy ±55° Filament Wound Pipes Under Internal Pressure,

Composite Science and Technology, Vol 65, pp. 703-708, 2004

102

[22] A.S. Kaddour, M.J. Hinton, P.D. Soden, Behaviour of ±45° Glass/Epoxy

Filament Wound Tubes Under Quasi-Static Biaxial Tension – Compression

Loading: Experimental Results, Composites Part B: Engineering, Vol 34, pp.

689-704, 2003

[23] F. Ellyin and M. Martens, Biaxial Fatigue Behaviour of a Multidirectional

Filament-Wound Glass-Fiber/Epoxy Pipe, Composites Science and

Technology, Vol 61, pp 491-502, 2001

[24] C. Kaynak, O. Mat, Uniaxial Fatigue Behavior of Filament Wound Glass-

Fiber/Epoxy Composite Tubes, Composites Science and Technology, Vol 61,

pp. 1833-1840, 2001

[25] J. Bai, P. Seeleuthner, and P. Bompard, Mechanical Behavior of ±55°

Filament-Wound Glass-Fibre/Epoxy-Resin Tubes: I. Microstructural

Analyses, Mechanical Behavior and Damage Mechanisms of Composite

Tubes Under Pure Tensile Loading, Pure Internal Pressure, and Combined

Loading, Composites Science and Technology, Vol 57, pp 141-153, 1997

[26] M.R. Etemad, E. Pask and C.B. Besant, Hoop Strength Characterization of

High Strength Carbon Fibre Composites, Composites, Vol 23, pp 253-259,

1992

[27] L. Parnas and N. Katırcı, Design of Fiber-Reinforced Composite Pressure

Vessels Under Various Loading Conditions, Composite Structures, Vol 58,

pp. 83-95, 2002

103

[28] P.M. Wild and G.W. Vickers, Analysis of Filament-Wound Cylindrical Shells

Under Combined Centrifugal, Pressure and Axial Loading, Composites Part

A, Vol 28A, pp. 47-55, 1997

[29] J.-S Park, C.-S. Hong, C.-G. Kim and C.-U. Kim, Analysis of Filament

Wound Composite Structures Considering the Change of Winding Angles

Through the Thickness Direction, Composite Structures, Vol 55, pp 63-71, ,

2002

[30] C. Gargiulo, M. Marchetti, and A. Rizzo, Prediction of Failure Envelopes of

Composite Tubes Subjected to Biaxial Loadings, Acta Astronautica, Vol 39,

pp 355-368, 1996

[31] M. Xia, K. Kemmochi and H. Takayanagi, Analysis of Filament-Wound

Fiber-Reinforced Sandwich Pipe Under Combined Internal Pressure and

Thermomechanical Loading, Composite Structures, Vol 51, pp 273-283,

2001

[32] X.-K. Sun, S.-Y. Du, and G.-D Wang, Bursting Problem of Filament Wound

Composite Pressure Vessels, International Journal of Pressure Vessels and

Piping, Vol 76, pp 55-59, 1999

[33] A. S. Kaddour, M. J. Hinton and P. D. Soden, Behaviour of ±45°

Glass/Epoxy Filament Wound Composite Tubes Under Quasi-Static Equal

Biaxial Tension–Compression Loading: Experimental Results, Composites

Part B: Engineering, Vol 34, pp 689-704, 2003

104

Paper on Characterization of Pressure Composite Tubes

Documents

Transcript of Paper on Characterization of Pressure Composite Tubes